T. Reti

7003943129

Publications - 33

On the relationships between the first and second Zagreb Indices

T. Reti

Publication Name: Match

Publication Date: 2012-12-01

Volume: 68

Issue: 1

Page Range: 169-188

Description:

The Zagreb indices introduced by Gutman and Trinajstić more than thirty years ago are graph-based molecular structure descriptors. The research and application of the Zagreb indices appears mainly in mathematical chemistry. In this paper we present some new inequalities related to the first and the second Zagreb indices. By introducing the notions of P-dominant graphs, and of the valency-functions of a graph, correspondences with the novel inequalities presented are discussed. In addition, we find examples characterizing the validity of Zagreb indices inequality and equalities for some particular classes of connected biregular graphs.

Open Access: Yes

DOI: DOI not available

On the constant difference of Zagreb Indices

Marko Milošević T. Reti Dragan Stevanović

Publication Name: Match

Publication Date: 2012-12-01

Volume: 68

Issue: 1

Page Range: 157-168

Description:

Let Φ(z), z ∈ ℤ, be the set of all connected graphs whose difference of the second and the first Zagreb index is equal to z. We show that Φ(z) contains exactly one element, a star, for z < -2, while it is infinite for z ≥ -2. Moreover, all elements of Φ(-2) and Φ(-1) are trees, while Φ(0), besides trees, contains the cycles only Constructions of new elements of Φ(z) from the existing ones are based on the existence of vertices of degree two. We further show that the only elements of J z≤0Φ(z), which do not contain vertices of degree two, are stars and the molecular graphs of 2,3-dimethylbutane and 2,2,3-trimethylbutane.

Open Access: Yes

DOI: DOI not available

Spectral properties of fullerene graphs

Tomislav Došlić T. Reti

Publication Name: Match

Publication Date: 2011-12-01

Volume: 66

Issue: 3

Page Range: 733-742

Description:

We use a result from the theory of geometric representation of graphs to show that the separator of a fullerene graph on n vertices cannot exceed 24/n, thus improving the best currently known upper bound of 1-3/n. The result is then combined with a recently established upper bound on the smallest eigenvalue of fullerene graphs to show that there are only finitely many Ramanujan fullerenes. That settles down a conjecture on fullerenes made by the Graffiti software.

Open Access: Yes

DOI: DOI not available

On the vertex degree indices of connected graphs

Tomislav Doslia T. Reti Damir Vukičević

Publication Name: Chemical Physics Letters

Publication Date: 2011-08-25

Volume: 512

Issue: 4-6

Page Range: 283-286

Description:

We introduce a family of invariants defined in terms of positive functions of degrees of vertices in a graph. A member of the family that measures the average degree of neighbors of vertices in a graph is then investigated for the predictive potential for stability in the class of generalized fullerenes. © 2011 Elsevier B.V. All rights reserved.

Open Access: Yes

DOI: 10.1016/j.cplett.2011.07.040

Remarks to the topological characterization of cellular systems

I. Zsoldos T. Reti

Publication Name: Journal of Geometry and Physics

Publication Date: 2011-08-01

Volume: 61

Issue: 8

Page Range: 1476-1478

Description:

In this note we discuss and solve an open problem (a conjecture) posed in a paper "On the combinatorial characterization of quasicrystals" published earlier in the Journal of Geometry and Physics. The conjecture proved is valid for the majority of space filling cellular systems (polycrystals, nanotubes, and fullerenes). © 2011 Elsevier B.V.

Open Access: Yes

DOI: 10.1016/j.geomphys.2011.03.016

Evaluation Of hardening performance of cooling media by using inverse heat conduction methods and property prediction

I. Felde T. Reti

Publication Name: Strojniski Vestnik Journal of Mechanical Engineering

Publication Date: 2010-04-28

Volume: 56

Issue: 2

Page Range: 77-83

Description:

A sequential numerical method for characterization of hardening performance of quenchants applied for steel quenching is outlined here. This novel method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. As a function of surface temperature the heat transfer coefficient, characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for the calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameters. The hardening performance of the media is evaluated by the estimated hardness of the specimen obtained by heat treatment. © 2010 Journal of Mechanical Engineering. All rights reserved.

Open Access: Yes

DOI: DOI not available

Extension of isothermal time-temperature parameters to non-isothermal conditions: Application to the simulation of rapid tempering

Janez Grum G. Sarmiento A. M. Deus I. Felde T. Reti R. Colas

Publication Name: Strojniski Vestnik Journal of Mechanical Engineering

Publication Date: 2010-04-28

Volume: 56

Issue: 2

Page Range: 84-92

Description:

A phenomenological method for constructing non-isothermal, generalized time-temperature parameters (GTT parameters) is presented. An analysis of the relationship between the various traditional isothermal time-temperature parameters has verified that the generalized Dorn-parameter is regarded to be the sole non-isothermal complex parameter to which a rigorous, physically well-founded interpretation is attributed. Possible applications of GTT parameters are illustrated by examples concerning the prediction of hardness change in quenched steels during rapid tempering treatments. © 2010 Journal of Mechanical Engineering. All rights reserved.

Open Access: Yes

DOI: DOI not available

Modeling of distribution of visible and non-visible graphite nodules embedded in the surface layer of ductile cast iron

Ágnes Csizmazia I. Czinege Mihaly Réger T. Reti

Publication Name: Materials Science Forum

Publication Date: 2010-01-01

Volume: 659

Issue: Unknown

Page Range: 453-458

Description:

The graphite nodule count and size distribution are important structural parameters in the quantitative characterization of the microstructure of ductile cast irons. In several cases, it is observed that local surface damages (cracks or microchip formations) are generated by the final manufacturing process (superfinishing operation), and these defects are originated basically from the hidden (invisible) graphite nodules located directly below surface. Based on measured data obtained by an image analyzer, a stereological model and a simulation algorithm have been developed to analyse the correspondances between the graphite morphology and the defect formation. This method makes it possible to establish a correlation between the microstructure parameters and the occurrence of local surface defects on ductile cast iron components. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/MSF.659.453

Evaluation of cooling characteristics of quenchants by using inverse heat conduction methods and property prediction

I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2010-01-01

Volume: 659

Issue: Unknown

Page Range: 153-158

Description:

A sequential numerical method for characterization of hardening performance of quenchants applied for steel quenching is outlined here. This novel method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. The heat transfer coefficient, as a function of surface temperature, characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameters. The hardening performance of the media is evaluated by the estimated hardness of the specimen obtained by heat treatment. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/MSF.659.153

Diffusion in electrodes used for resistance spot welding of galvannealed steel

Martha P. Guerrero-Mata Patricia Zambrano I. Felde Mihaly Réger Maribel De La Garza T. Reti R. Colas

Publication Name: Defect and Diffusion Forum

Publication Date: 2010-01-01

Volume: 297-301

Issue: Unknown

Page Range: 300-307

Description:

A study was carried out on Zr-Cr bearing copper electrodes used for resistance spot welding of galvannealed steel strips. One electrode exhibited a series of well-defined layers in which Zn diffused to form β- and γ-brasses; an external layer containing iron was detected in this electrode. Another electrode that exhibited a high degree of damage did not exhibited continuous Zn-diffusion layers in all places, moreover, the Fe-containing layer was either removed, or had it grown to a high extent in some places; the occurrence of Cu-rich particles embedded within the Fe containing layer was observed. Multiple cracks were observed within the γ brass layer in both electrodes. The difference in the observed behaviour of the electrodes can be attributed to a difference in the characteristics of the galvannealed coating of the strips, as the first electrode was used to weld strips in which the layer corresponding to the γ phase was well developed, whereas the second electrode was used to weld strips with only an incipient layer. It can be concluded that growth of the γ phase changes the thermophysical properties of the zinc coating, affecting the temperature profile during spot welding. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/DDF.297-301.300

Classification of fullerene isomers using local topological descriptors

Enikö Bitay István László Tomislav Došlić T. Reti

Publication Name: Materials Science Forum

Publication Date: 2010-01-01

Volume: 659

Issue: Unknown

Page Range: 447-451

Description:

A method for the structural classification of fullerenes via graph invariants is presented. These graph invariants (called edge-parameters) represent the 9 different types of bonds existing in fullerenes between two neighbouring carbon atoms and they are also applicable to classify the fullerene isomers into equivalence classes. Discriminating performance of edge-parameters has been tested on the sets of C40 and C66 fullerene isomers. It is shown that the stability of C40 and C66 isomers can be efficiently predicted using a novel topological descriptor (Ω) defined as a function of four appropriately selected edge parameters. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/MSF.659.447

Characterisation of hardening performance of quenchants by integrated numerical method

I. Felde T. Reti

Publication Name: International Heat Treatment and Surface Engineering

Publication Date: 2008-06-01

Volume: 2

Issue: 2

Page Range: 55-59

Description:

An integrated numerical technique for evaluation of hardening performance of cooling media applied for steel quenching is outlined. The newly developed method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. The heat transfer coefficient as a function of surface temperature characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameter. The hardening performance of media is evaluated by the estimated hardness of specimens obtained by heat treatment. © 2008 IHTSE Partnership.

Open Access: Yes

DOI: 10.1179/174951508X318404

Selection of tool materials for cold forming operations using a computerized decision support system

J. Gram I. Czinege I. Felde T. Reti D. Y. Ju

Publication Name: Proceedings of the 17th Ifhtse Congress

Publication Date: 2008-01-01

Volume: 2

Issue: Unknown

Page Range: 773-775

Description:

A computerized decision support system (DSS) is outlined which is designated primarily to selcct the proper tool steel grades for various cold forming operations. This computerized system contains four data base: data base of cold forming operations and tools, of work materials, of cold forming tool materials and of wear resistant PVD coatings. The decision strategy makes it possible to select appropriate tool materials taking into consideration their most important material properties (wear resistance, toughness, compressive yield strength, tempering resistance, dimensional stability, machinability, and material price). The practical advantages of the developed decision support system are demonstrated on example.

Open Access: Yes

DOI: DOI not available

Analysis of a numerical method developed for estimation of the heat transfer coefficient obtained during quenching

G. Sarmiento A. M. Deus B. Smoljan I. Felde T. Reti

Publication Name: Proceedings of the 17th Ifhtse Congress

Publication Date: 2008-01-01

Volume: 2

Issue: Unknown

Page Range: 816-819

Description:

A numerical method for prediction of the Heat Transfer Coefficient (HTC) obtained during quenching is described in this paper. An iterative regularization algorithm is used to solve the inverse problem under study. The unknown HTC function is approximated by polynomial functions of surface temperature. The numerical method developed is verified by using the temperature data measured with a JIS silver probe.

Open Access: Yes

DOI: DOI not available

Simulation of 3-dimensional cell population growth processes in polyhedral cellular systems

I. Zsoldos T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 579-590

Description:

In order to simulate the polyhedral grain nucleation in alloys, 3-D cell population growth processes are studied in space-filling periodic cellular systems. We discussed two different methods by which space-filling polyhedral cellular systems can be constructed by topological transformations performed on "stable" 3-D cellular systems. It has been demonstrated that an infinite sequence of stable periodic space-filling polyhedral systems can be generated by means of a simple recursion procedure based on a vertex based tetrahedron insertion. On the basis of computed results it is conjectured that in a 3-D periodic, topologically stable cellular system the minimum value of the average face number 〈f〉 of polyhedral cells is larger than eight (i.e. 〈f〉 > 8). The outlined algorithms (which are based on cell decomposition and/or cell nucleation) provide a new perspective to simulate grain population growth processes in materials with polyhedral microstructure.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.579

On the topological characterization of 3-D polyhedral microstructures

Ágnes Csizmazia I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 563-570

Description:

To characterize topologically the polycrystalline microstructure of single-phase alloys computer simulations are performed on 3-dimensional cellular models. These infinite periodic cellular systems are constructed from a finite set of space filling convex polyhedra (grains). It is shown that the appropriately selected topological shape factors can be successfully used for the quantitative characterization of computer-simulated microstructures of various types.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.563

Prediction of fullerene stability using topological descriptors

Enikö Bitay T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 439-448

Description:

In recent years, several attempts have been made to characterize the geometric structure of fullerenes by means of topological shape factors in order to predict their physical properties and stability. In this paper, we present a simple method to estimate the stability of fullerenes on the basis of quantitative topological criteria. This approach is based on the concept of the generalized combinatorial curvatures defined on the set of simple graphs embedded on a closed surface without boundary (sphere, torus, projective plane, Klein bottle). It is shown that starting with the computed generalized combinatorial curvatures several novel topological indices can be generated. From computations performed on a set of C40 and C60 fullerenes, we concluded that the four topological shape factors tested (Λ(-1), Ω(-1), Λ(1) and Ω(1)) could be successfully used to preselect the most stable fullerene isomers.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.439

On the temperature rate dependent transformation processes

L. Costa I. Czinege I. Felde T. Reti R. Colas

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 571-578

Description:

Kinetic models of new types are suggested which are designated primarily to predict the progress of non-isothermal transformations occurring during rapid heating and cooling in alloys. A common feature of each model outlined is that it takes into account not only the varying temperature but also the rate of temperature change on the transformation rate of the process. The two models represented by differential equations are generated by using the concept of virtual kinetic parameters, which can be determined from non-isothermal experiments only. A key property of the virtual parameter "p" involved in the transformation rate equations is that it quantitatively characterizes the temperature rate dependence of the non-isothermal reaction.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.571

Evaluation of steel hardenability by JM®-test

D. Iljkic N. Tomasic G. E. Totten B. Smoljan I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 607-614

Description:

The modified Jominy-test was designed for prediction of hardenability of high-hardenability tool steels and possibility of application of modified Jominy-test in computer simulation of quenching of high-hardenability tool steels has been investigated. Because of high hardenability there are limits in application of original Jominy-specimen in simulation of quenching of steels. The performance of investigated modified Jominy-test in simulation of quenching of high-hardenability tool steels was estimated by comparison of cooling curves of modified Jominy-specimen (JM®-specimen) and cylindrical specimen. The influence of dimension of JM®-specimen on cooling curves has been investigated. The time of cooling, t8/5 relevant for results of quenching was predicted. Modified Jominy-test can be applied in simulation of quenching of steel with higher hardenability rather than original Jominy-test.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.607

Laser powder deposition of tool steels: Strategies leading to homogeneous parts

L. Costa T. Reti R. Vilar

Publication Name: Materials Science Forum

Publication Date: 2006-01-01

Volume: 514-516

Issue: PART 1

Page Range: 739-743

Description:

The microstructure and properties of tool steel parts built by laser powder deposition (LPD) depend considerably on the build-up strategy and on the processing parameters used. This dependence can lead to inconsistent results which may limit the widespread acceptance of LPD. There is, thus, a need for efficient process optimisation tools that take into consideration the complex phase transformations that may occur during the part build-up process and their effect on final properties. A model coupling finite element heat transfer calculations with transformation kinetic theory has been developed, which allows the microstructure and property distributions in parts produced by LPD to be predicted. Application of this model to the deposition of tool steels not only explains the origin of the heterogeneous distribution of properties usually mentioned in the literature but also allows designing build-up strategies that consistently lead to homogeneous, high quality parts. Its application to the study of the influence of substrate pre-heating and idle time between the deposition of consecutive layers is illustrated in the present paper.

Open Access: Yes

DOI: 10.4028/www.scientific.net/msf.514-516.739

On the topology of two dimensional generalized cell systems

I. Zsoldos J. Janik T. Reti

Publication Name: Recent Advances in Multidisciplinary Applied Physics

Publication Date: 2005-12-01

Volume: Unknown

Issue: Unknown

Page Range: 559-564

Description:

No description provided

Open Access: Yes

DOI: 10.1016/B978-008044648-6.50085-9

Rapid tooling by laser powder deposition: Process simulation using finite element analysis

L. Costa A. M. Deus T. Reti R. Vilar

Publication Name: Acta Materialia

Publication Date: 2005-08-01

Volume: 53

Issue: 14

Page Range: 3987-3999

Description:

Laser powder deposition (LPD) is a rapid manufacturing process, whereby near-net-shape components are fabricated by the successive overlapping of layers of laser melted and resolidified material. As new layers of material are deposited, heat is conducted away from recently resolidified material, through the previously deposited layers, inducing cyclic thermal fluctuations in the part as it is built up. These thermal cycles can activate a variety of metallurgical phenomena, such as solid-state transformations, leading to a progressive modification of the material's microstructure and properties. Since the thermal history of the material in the deposited part will differ from point to point and depends on the deposition parameters and build-up strategy, the finished part may present complex distributions of microstructure and properties. In order to achieve the best properties, the deposition process must be optimized and, given its complexity, this optimization can only be effectively done using mathematical simulation methods. In this paper a thermo-kinetic LPD model coupling finite element heat transfer calculations with transformation kinetics and quantitative property-structure relationships is presented. This model was applied to the study of the influence of substrate size and idle time between the deposition of consecutive layers on the microstructure and hardness of a ten-layer AISI 420 steel wall built by LPD. The results show that the thermal history and, hence, the microstructure and properties of the final part, depend significantly on these parameters. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Open Access: Yes

DOI: 10.1016/j.actamat.2005.05.003

Partial electron beam hardening of cast iron camshafts

Ágnes Csizmazia Miklós Horváth István Oláh T. Reti

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 447-452

Description:

In order to improve the local surface properties (hardness, wear and contact fatigue resistance) of cast iron camshafts, detailed experiments with partial electron beam hardening have been performed. It was found that the required case depth of 0.3-0.5 mm and surface hardness of 600-700 HV can be achieved by using appropriately selected, computer-controlled processing parameters (angular speed, specific energy input, beam deflection). © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.447

A possible extension of the Aboav-Wealre law

I. Zsoldos T. Reti

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 389-398

Description:

The semi-empirical Aboav-Weaire law is generally used to characterize the local topological correlation between the neighbor cells in 2D space-filling random cellular system. Starting with a possible generalization of the Aboav-Weaire law, this paper presents a new method, which is designated primarily to the topological characterization of finite cellular systems defined on an unbounded, closed and orientable surface, and composed of a finite set of combinatorial polygons. It is demonstrated that using two simple topological parameters (AR and ER) derived from the extended Aboav-Weaire equation, the local structure and the stability of polyhedral fullerenes can be efficiently evaluated on the basis of quantitative criteria. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.389

Topological characterization of finite cellular systems represented by 4-dimensional polytopes

Károly Boroczky T. Reti

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 381-388

Description:

A 4-dimensional polytope composed of space filling three-dimensional polyhedra (cells) can be considered as a finite cellular system. It is verified that the fundamental equations of the cell statistics, (i.e. the Weaire identity and the Aboav-Weaire law) can be extended to 4-dimensional finite cellular systems represented by 4-polytopes. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.381

Simulation of phase transformations in steel parts produced by laser powder deposition

L. Costa A. M. Deus I. Felde R. Colaço T. Reti R. Vilar

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 315-320

Description:

Multilayer laser powder deposition is being used for the rapid manufacturing of fully dense near net shape components in a wide variety of materials. In this process parts are built by overlapping consecutive layers of a laser melted material. As a result of this overlapping, the material in each layer will undergo successive thermal cycles as new layers are deposited. Despite their short duration, these thermal cycles can activate solid-state transformations that lead to progressive modification of the microstructure and properties of the material. Since the thermal history of the material in the deposited part will differ from point to point, the part will present a complex and heterogeneous microstructure, and properties that differ from point to point. Given that the microstructure and property distribution in steel parts produced by laser powder deposition can only be predicted by modelling, a three-dimensional thermo-kinetic finite element model of laser powder deposition of tool steels was developed, In the present work this model was applied to the study of the influence of substrate size on the microstructure and properties of a six-layer wall of AISI 420 tool steel. The results show that the temperature field depends significantly on the size of the substrate, leading to distinct microstructures and properties in the final part. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.315

Numerical methods for safeguarding the performance of the quenching process

S. Sarmiente I. Felde S. Segerberg T. Reti J. Bodin

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 335-340

Description:

ivf SmartQuench™ - a new system for testing and evaluation of quenching media and quenching systems - has recently been introduced by IVF. One of the system main features is an advanced computer software, which provides flexible evaluation of quenchants in many respects. The abilities of the computer program is underlined. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.335

On the physical and mathematical interpretation of the isokinetic hypothesis

T. Reti

Publication Name: Journal De Physique IV JP

Publication Date: 2004-12-01

Volume: 120

Issue: Unknown

Page Range: 85-91

Description:

Based on the investigation of additive kinetic differential equations it is shown that the concept of the traditional isokinetic hypothesis defined by Christian can be easily generalized. By introducing the notion of the weakly isokinetic process, it is verified that the extended isokinetic model can be expressed in terms of an integro-differential equation. A special property of this integro-differential equation is that its right-hand side includes such state-parameters, which are determined by the whole temperature history (i.e. each state parameter is a functional of the time-temperature function, or any other selected state functions). © EDP Sciences.

Open Access: Yes

DOI: 10.1051/jp4:2004120009

Geometric construction of carbon nanotube junctions

I. Zsoldos T. Reti A. Szasz Gy Kakuk

Publication Name: Modelling and Simulation in Materials Science and Engineering

Publication Date: 2004-11-01

Volume: 12

Issue: 6

Page Range: 1251-1266

Description:

In this work we demonstrate that carbon nanotube junctions with an optional number, type (zigzag and/or armchair) and diameter of tubes can exist. We show a method for geometric construction of their models.

Open Access: Yes

DOI: 10.1088/0965-0393/12/6/017

Residual stresses in carburised, carbonitrided and case-hardened components (Part 2)

T. Reti

Publication Name: Heat Treatment of Metals

Publication Date: 2004-03-11

Volume: 31

Issue: 1

Page Range: 4-10

Description:

An overview is given of the significant progress in research focused on the assessment of residual stress effects in case-hardened components. Focus is on relevant computational models intended to simulate stress evolution during heat treatment.

Open Access: Yes

DOI: DOI not available

Residual Stresses in Carburised, Carbonitrided and Case-hardened Components (Part 1)

T. Reti

Publication Name: Heat Treatment of Metals

Publication Date: 2003-12-08

Volume: 30

Issue: 4

Page Range: 83-96

Description:

The assesment of residual stress effects in carburised, carbonitride and case-hardened components was discussed. The development of computational models and procedures, which were applied to the simulation of the stress-evolution processes during heat treatment was also discussed. Shot peening, the most versatile method of producing residual stresses was studied. The influence of microstructure and residual stresses on crack initiation and propagation was discussed.

Open Access: Yes

DOI: DOI not available

Tempering effects in steel parts produced by additive fabrication using laser powder deposition

L. Costa A. M. Deus R. Colaço T. Reti R. Vilar

Publication Name: Virtual Modelling and Rapid Manufacturing Advanced Research in Virtual and Rapid Prototyping

Publication Date: 2003-12-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Laser processed tool steels present a metastable structure generally containing martensite and an extremely large proportion of retained austenite as compared to conventionally treated steel, which affects considerably the properties of the material. In rapid tooling by laser powder deposition, as consecutive layers of material are deposited to generate a 3D object, the material in previously deposited layers is submitted to successive thermal cycles, which destabilise retained austenite, leading to its transformation to martensite. Also, the martensite present in these layers will progressively decompose by tempering when the material is reheated. As a result, the properties of the material are progressively modified as the object is built-up. The evolution of the microstructure and properties of tool steels during laser freeform manufacturing is extremely difficult to study experimentally, due to the complexity of the transformations involved and the heterogeneity of the material and of the applied thermal field, hence modelling presents clear advantages in the optimization of part build-up strategy. In the present work, a model of the phase transformations resulting from the successive overlap of clad layers based on the coupling of finite element calculations of the time-dependent temperature distribution with transformation kinetics is described. The model was used to predict the evolution of properties and final property distribution in a martensitic stainless steel component produced by laser powder deposition.

Open Access: Yes

DOI: DOI not available

A simple technique to estimate the processing window for laser clad coatings

K. Zoltan L. Costa B. Verö I. Felde R. Colaço T. Reti R. Vilar

Publication Name: International Surface Engineering Congress Proceedings of the 1st Congress

Publication Date: 2003-12-01

Volume: Unknown

Issue: Unknown

Page Range: 237-242

Description:

A semi-empirical method for selecting the processing parameters of laser cladding is proposed. This phenomenological approach uses simple mathematical formulae, derived from a statistical analysis of measured data, to relate the laser cladding parameters with the geometric features of the clad track. Given the required clad height and available laser beam power, the proposed method allows one to calculate values of the scanning speed and powder feed rate which are used to obtain low dilution, pore free coatings, fusion bonded to the substrate. To illustrate the application of this method, variable powder feed rate laser cladding experiments were carried out with Stellite 6 powder on mild steel substrates. In this technique the laser beam power and radius and the processing speed are kept constant, while the powder feed rate is varied along a single track length according to a specified linear function. The expressions derived from the model were used to plot the experimental data in a coherent manner, revealing the combined role of the different processing parameters.

Open Access: Yes

DOI: DOI not available