A. M. Deus

6506560948

Publications - 5

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

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

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

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

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