TMS 2006 135th Annual Meeting & Exhibition

March 12-16, 2006

The conference held in San Antonio, Texas was attended by:

Graduate Students: Olga Karabelchtchikova, Yao Zhou
Professors: Diran Apelian, Yiming "Kevin" Rong, Richard Sisson, Jr.
Research Assistant Professor: Diana Lados

Prof. Diran Apelian, Director of WPI's Metal Processing Institute, received two of the highest honors from the Minerals, Metals and Materials Society (TMS).

Prof. Richard D. Sisson, Jr. was one of the Program Organizers of the Multicomponent-Multiphase Diffusion Symposium in Honor of Mysore A. Dayananda, his work and 70th birthday. The symposium held six sessions: Phenomenology (Prof. Sisson co-chaired), Modeling and Simulation, Metals and Alloys, Intermatallics and Ceramics, Industrial Applications, and Surfaces and Interfaces.

Papers presented:

Carbon Diffusion in Steels-a Numerical Analysis based on Direct Integration of the Flux
Modeling the Heat Treatment of Age-Hardenable Cast Aluminum Alloys
Optimization of Load Arrangement and Thermal Cycle Design for Time and Energy Efficient Heat Treatment Process for Aluminum Castings
Parameters and Key Trends Effecting Fatigue Crack Growth- A Tribute to Professor Arthur J. McEvily's Contributions
Fatigue Crack Growth in AI-Si-Mg Cast Alloys: Microstructural and Processing Considerations

Carbon Diffusion in Steels-a Numerical Analysis based on Direct Integration of the Flux

Authors:

Olga Karabelchtchikova, Richard D. Sisson, Jr.

In the early 1970s, Professor Dayananda developed a technique of direct integration of fluxes over distance from the concentration profiles in vapor-solid diffusion couples. This integration allowed determination of concentration dependent atomic mobilities and diffusion coefficients. As part of a project to control and optimize the industrial carburization process in mild and low-alloyed steels, this analysis was applied to several commercial grade carbuized steels to determine the effect of alloy composition on their atomic mobility and carbon diffusion in the Austenitic phase. While carbon flux and therefore surface carbon content vary with time during single-stage carburizing even with a fixed carbon potential in the atmosphere, a mass balance at the gas-solid interface must serve as boundary condition. Furthermore, the analysis was applied to determine the characteristic surface mass transfer coefficient and carbon mobilities in several grades of steel. The results were compared with previous determinations and predictions reported in literature.

Modeling the Heat Treatment of Age-Hardenable Cast Aluminum Alloys

Authors:

Richard Dean Sisson, Shuhui Ma, Md. Maniruzzaman

The effects of solutionizing times and quenching rates on the microstructure and mechanical properties of age-hardenable cast aluminum alloys (i.e. 319 and A356) has been experimentally investigated with Jominy End Quench Bars and theoretically analyzed using Quench Factor Analysis. The results indicate that the solutionizing time for metal mold cast alloys can be reduced from 12 hours to less than 4 hours depending on the casting microstructure and secondary dendrite arm spacing. The Jominy End Quench experiments revealed that these alloys are not very quench sensitive with alloy A356 being more quench sensitive than 319. Quench Factor Analysis proved to applicable to these cast alloys and a good predictor of hardness. The results are discussed in terms of alloy microstructure including Silicon spheroidation and hardening precipitate development.

Optimization of Load Arrangement and Thermal Cycle Design for Time and Energy Efficient Heat Treatment Process for Aluminum Castings

Authors:

Yao Zhou, Jinwu Kang, Yiming Rong

Abstract

Heat treatment of aluminum castings is a time and energy consuming process. Based on the process model developed in our previous research, the heat treatment processes can be simulated, evaluated, and optimized. This paper considers two ways to reduce cycle time and energy consumption by optimizing load arrangement and thermal cycle.

Different load arrangements result in different temperature profiles, which further lead to different cycle times and energy consumption. By simulating the processes and evaluating them in terms of relative cost function for candidate load arrangement designs, optimum design can be determined. Thermal cycle can be such designed that the furnace is first heated to a temperature above soaking temperature so as to heat the load faster. Then, the furnace is brought back to the soaking temperature at a proper time so that the load finally rises to the soaking temperature without overheating. This “proper time” is critical and is calculated and controlled by the algorithms. Comparative study shows that the proposed optimizations in load arrangement and thermal cycle design yield significant time and energy saving.

Parameters and Key Trends Effecting Fatigue Crack Growth- A Tribute to Professor Arthur J. McEvily's Contributions

Authors:

Diana A. Lados and Paul C. Paris

Abstract

The early 1950s led to high performance aluminum skinned aircraft for which metal fatigue and fatigue crack growth became extremely important considerations. Virtually, no significant range of data on fatigue crack growth existed prior to McEvily's work, and controlling parameters were left to be further developed. His pioneering work allowed others to resolve some of the critical issues, and yet a few still remain open even today. This discussion will trace historical milestones in the field, as well as some more recent investigations, with the intention of exposing the major trends. Finally, a new methodology for analyzing fatigue crack growth load-displacement records (beyond ASTM) determining "effective stress intensity factor ranges", the major mechanical cause of crack growth, is discussed.

Microstructural Mechanisms Controlling Fatigue Crack Growth in Al-Si-Mg Cast Alloys

Authors:

Diana A. Lados, Diran Apelian, Peggy E. Jones, J. Fred Major

Abstract

Fatigue crack growth behavior of long and small cracks was investigated for hypoeutectic and eutectic Al-Si-Mg cast alloys. Crack growth response in the near-threshold regime and Regions II and III was related to microstructural constituents namely primary -Al dendrites and volume fraction and morphology of eutectic Si. Long cracks thresholds are dictated by microstructure/roughness induced closure. The small crack threshold behavior is explained through closure independent mechanisms, specifically through the barrier effects of characteristic microstructural features specific to each alloy. In Regions II and III changes in fracture surface appearance were associated with different crack growth mechanisms at the microstructural scale. The extent of the plastic zone ahead of the crack tip was successfully used to explain the observed changes in crack growth mechanisms.

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