TMS 2005 134th Annual Meeting & Exhibition

February 13-17, 2005

The conference held in San Francisco, CA was attended by:

Graduate Students: Olga Karabelchtchikova
Professors: Diran Apelian, Makhlouf Makhlouf, Richard Sisson, Jr.
Research Scientists: Libo Wang, Sujoy Chaudhury
Post Doc: Diana Lados

Papers presented:

Metals Industry"
"Influence of Temperature and Alloying Elements on Fluidity of Al-Si Alloys,"
"Fluidized Bed Heat Treatment of Cast Al Alloys"
"Controlled Diffusion Solidification - Manufacturing Quality Net Shaped Al Based Wrought Alloy Parts,"
"Mechanism of Eutectic Solidification of Aluminum-Silicon Alloys"
"Chemical Modification of the Morphology of the Eutectic Phases in Hypoeutectic Aluminum-Silicon Alloys"
"Carburization Process Modeling"
"Crystallographic Texture of EB-PBD TBCs on Stationary Flat Surfaces in a Multiple Ingot Chamber"
"Investigation of Residual Stresses Superposition of D2 Dies due to Heat Treatment and Multipass Grinding"
"Modeling of Residual Stresses Via Grinding Dynamics Using Second-Order Damping System"

Metals Industry

Authors:

Diran Apelian

Summary not available

Influence of Temperature and Alloying Elements on Fluidity of Al-Si Alloys

Authors:

Marisa Di Sabatino, Sumanth Shankar, Diran Apelian, Lars Arnberg

Abstract

The goal of the work is to study the influence of casting temperature and four alloying elements: Mg, Ti, Fe and Sr, on fluidity of Al-7wt% Si alloys. fluidity of the alloys awas measured using a fluidity mould produced by N-Tec Ltd., U.K. The experiements were designed using three othrogonal L8 Taguchi matrices. Each of the four alloying elements and the casting temperature was an independent variable with two levels. Three interactions between the variables were identifed and analyzed. The two levels of Mg were 0.03wt.% and 0.45 wt.%; Ti levels were 0 and 0.2%; Sr at 0 and 0.023 wt%; and Fe levels were 0.06% wt% and 0.24.%. Superheats were 70 C and 130 C over the respective liquidus temperatures of the experimental alloys. The main effect of each of the independent variables on the fluidity was quantified and Analysis of Variance(ANOVA) was performed on the experiment matrix. The results were verified and validated to ensure robustness of the experiement design. In addition to the Taguchi design of experiments show that casting temperature had the most pronounced influence on fluidity of the molten metal. Among the alloying elements chosen, only MG had an appreciable effect on fluidity. Increasing Mg in the melt from 0 to 0.45 wt.% showed a decrease in fluidity of the molten metal. The results of the fluidity experiments on the additional five melt systems show that silicon has a significant effect on fluidity. The variation of fluidity among families of Al-Si alloys is more pronounced that the variation within a particular family of alloy such as 356, which implies that minor changes in composition within a family of Al-Si alloy does not influence fluidity significantly.

Fluidized Bed Heat Treatment of Cast Al Alloys

Authors:

Sujoy Chaudhury, Diran Apelian

Abstract

Improved mechanical properties in cast Al alloys are often achieved through heat treatment comprising of solution heat treatment, quenching, and ageing successively. With the impetus to be cost effective, it is imperative to reduce the long heat-treating times needed (i.e., up to 15-20 hours) without any reduction in performance. Fluidized beds provide an attractive heat treating technology for cast components with more effective energy transfer and thereby reducing the heat treatment time and enhance productivity. However, typical fluidized bed units are batch systems; therefore, further reductions in cycle time may be possible by using in-line continuous fluidized beds. In this paper, we will review the fundamentals of fluidized beds, highlight their advantages and examine applications of fluidized beds to heat treat cast Al-Si-Mg, and Al-Si-Cu-Mg alloys. Mechanical properties data along with the resultant microstructure as a result of extensive trials with fluidized bed technology will be reviewed and discussed.

Controlled Diffusion Solidification - Manufacturing Quality Net Shaped Al Based Wrought Alloy Parts

Authors:

Deepak Saha, Sumanth Shankar, Diran Apelian, Makhlouf Makhlouf

Abstract

Aluminum combined with differing percentages of other metals such as silicon, copper, magnesium, and manganese form alloys that are used in may domestic, automotive and aerospace applications. Net shape manufacturing of wrought alloys (via casting) has been prohibitive due the proclivity of these alloys to "hot tears". Hot tearing tendency coupled with coherency temperature, that is close to the liquidus temperatures, lead to the development of cracks in the final "as cast" structure. The microstructure of wrought allys is predominantly dendritic, and by altering the dendritic morphology to a globular one (providing a continuous interdendritic liquid network) one can considerably reduce the hot tearing issues. A novel method has been developed at WPI, temed Conrolled Diffusion Solidificatin or CDS. In this process, two precursor liquid alloys of precisely controlled chemistry and temperature are mixed to produce a predetermined alloy composition. CDS provides an effective process for the net shape manufacturing of these alloys. The CDS process is discussed and reviewed; results from industrial trials utilizing a variety of different casting processes are presented, along with the resultant microstructural data and mechanical properties.

Mechanism of Eutectic Solidification of Aluminum-Silicon Alloys

Authors:

Sumanth Shankar, Makhlouf Makhlouf

Abstract

A mechanism is presented to explain the formatin of the eutectic phases in Al-Si hypoeutectic alloys. The mechanism is supported with results of non-equilibrium thermal analyses, and microstructure evidence obtained from optical, scanning and transmission electron microscopy, as well as selected area electron diffractin analyses and elemental x-ray mapping, in addition to results of high temperature rheological measurements performed on Al-Si alloy samples of precisely controlled chemistry.

Chemical Modification of the Morphology of the Eutectic Phases in Hypoeutectic Aluminum-Silicon Alloys

Authors:

Sumanth Shankar,Makhlouf Makhlouf

Abstract

A mechanism is presented to explain the chemical modification of the morphology of the eutectic phases in Al-Si hypoeutectic alloys. The mechanism is supported with results of non-equilibrium thermal analyses, and microstructure evidence obtained from optical, scanning and transmission electron microscopy, as well as selected area electron diffraction analyses and elemental x-ray mapping, in addition to results of high temperature rheaological measurements performed on Al-Si alloy samples of precisely controlled chemistry.

Carburization Process Modeling

Authors:

Richard D. Sisson, Jr.

Abstract

A brief history of carburization process modeling will be presented followed by an assessment of the current status of our modeling capability. The database needs will be addressed in terms of the temperature and composition dependence of carbon diffusion coefficients as well as the surface mass transfer of coefficients as a function of temperature, gas composition and steel surface condition. The sensitivity of case depth to process parameters will also be discussed.

Crystallographic Texture of EB-PBD TBCs on Stationary Flat Surfaces in a Multiple Ingot Chamber

Authors:

Jeremy Bernier, G. Levan, Sudha Bose, Md. Maniruzzaman, Richard D. Sisson, Jr.

Abstract

The crystallographic texture of EB-PVD TBCs (7 wt% Y203) deposited in two ingot chamber has been experimentally determined by comparing pole figure data with measured column growth angles. It was found that the coating deposited on a flat surface directly above an ingot exhibited <220> texture. Coatings deposited between the ingots and off of the centerline exhibited <311> texture. Coating deposited at the far corners of coating chamber revealed a <110> fiber texture or <311> single crystal type texture. The microstructures of specimen cross sections reveal that column growth angle and vapor incidence angles are in reasonable agreement and that the columns grow towards the closest ingot. These results are discussed in tems of substrate temperature and vapor incidence angles.

Investigation of Residual Stresses Superposition of D2 Dies due to Heat Treatment and Multipass Grinding

Authors:

Olga Karabelchtchikova, Iris V. Rivero

Abstract

The study investigated residual stresses behaviors and their superposition effect in D2 dies for thread-rolling applications. A nested factorial experiment was applied to test hypotheses that the residual stresses profiles change due to combination of heat treatment and multipass grinding operations, and that certain patterns can be derived due to the memory relationship between pre-existing and final residual stresses distributions. The amount of the retained austenite along with residual stresses in variation with depth was measured using x-ray diffraction technique. Statistical analyses indicate that the proposed hypotheses hold. Residual stresses distributions as well as tensile peak location were found to be significantly influenced by the treatment parameters used. Unique characteristic patterns in the residual stresses profiles were observed due to multipass grinding technique across all experimental conditions. This finding suggested a plausible memory relationship between the cutting passes, and the causes of the foregoing results are further proposed and discussed.

Modeling of Residual Stresses Via Grinding Dynamics Using Second-Order Damping System

Authors:

Olga Karabelchtchikova, Simon M. Hsiang

Abstract

A second-order system is proposed to model residual stresses (RS) distributions under various heat treatment procedures and the assumed second-order grinding dynamics. The study was motivated to (1) predict the magnitude of the RS and tensile peak location, and (2) establish superposition relationship in the RS distribution due to number of grinding passes.

Grinding dynamics was represented as a lumped system composed of spring-mass-damper of the grinding machine and damper-stiffness of the workpiece. A nested factorial experiment of 18 conditions with 3 levels of tempering factor, 2 levels of grinding conditions and 3 multipass grinding levels was used for the model development and validation. The parameters of each condition were then optimized by using auto-regressive system identification.

The proposed model depicts changes of the complex experimental treatment conditions and demonstrates a good estimation of the subsurface RS distribution. With only one parameter involved, the prediction elucidates grinding dynamics and supports a theory of the heat treatment and grinding effects on the material characteristics.

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Last modified: Nov 02, 2005, 14:22 EST