David L. Lawrence Convention Center

Pittsburgh, Pennsylvania, USA


October  8 - 12, 2017

Members who attended:

Professors: Richard D. Sisson Jr., Danielle Cote,

Graduate Students: Caitlin Walde, Kyle L. Fitzpatrick-Schmidt, Farzaneh Farhadi, Anbo Wang, Haixuan Yu, Xiaoqing Cai, Lei Zhang, Yuan Lu, Derek Tsaknopoulos


Characterizing the Effect of Thermal Processing on Powder Al Alloys for Additive Manufacturing Applications

Caitlin Walde1; Danielle Cote1; Richard Sisson1; Victor Champagne2; 1Worcester Polytechnic Institute 2US Army Research Laboratory

Gas-atomized metallic powders are commonly used in additive manufacturing processes. Research has shown that, for certain AM techniques, the chemistry and microstructural properties of the feedstock powder significantly affect the properties of the consolidated material. Understanding the powder characteristics before use in additive manufacturing can lead to optimizing properties of additively manufactured materials as well as determining the recyclability of feedstock powders. This research studies the effect of various heat treatment processes on the characteristics and microstructural evolution of powder aluminum alloys 2024, 6061, and 7075. Treatment times and temperatures were guided by thermodynamic and kinetic modeling. Optical microscopy, scanning electron microscopy, and nanohardness were used to evaluate each condition. Experimental results are compared to those predicted through modeling.

Dissolution of Secondary Phases in Al Alloys using DICTRA Simulations

Kyle L Fitzpatrick-Schmidt1; Danielle Cote1; Richard Sisson1; Victor Champagne2; 1Worcester Polytechnic Institute 2US Army Research Laboratory

Secondary phases can strongly influence the mechanical properties of a material. In this work, the dissolution of these phases, as well as homogenization of chemical segregation, is studied. The optimum heating time and temperature for these processes must be determined, but can be challenging when done experimentally by trial and error. The use of thermodynamic and kinetic modeling to determine the time and temperature parameters can lead to efficient determination of ideal homogenization and solutionization processes. This work focuses on the use of DICTRA simulations to calculate optimized homogenization and solutionization times and temperatures to dissolve chemical segregation and secondary phases, particularly in aluminum alloy powders. These simulations will be experimentally verified using scanning and transmission electron microscopy.

Liquid-solid Diffusion in Liquid Aluminum/Stainless Steel

Farzaneh Farhadi1; Richard D. Sisson1; 1Center for Heat Treating Excellence (CHTE), Worcester Polytechnic Institute (WPI)

An experimental evaluation has been initiated between liquid aluminum and a series of stainless steels. Diffusion kinetics in solid and liquid phases were investigated as well as morphology and phase development of intermetallic compounds as a function of time. This paper presents results of RA330 stainless steel hot-dipped in both pure aluminum at 700oC temperature for 4, 6, and 10 minutes. To have a better understanding of the diffusion kinetics, the same experiments were performed by dipping 1018 steel and pure Nickel in the Aluminum. Microstructures and diffusion kinetics were investigated using Scanning electron microscopy, X-ray diffraction analysis, Electron backscatter diffraction, Energy Dispersive X-Ray Spectroscopy, and Optical Emission Spectrometry. Computational analysis methods were used to assist in predicting the diffusion coefficients, growth kinetics, stable phases, and phase transformations. A good correspondence between the experimental and quantitative results is obtained.

Life Extension of RA602CA by Aluminizing Furnace

Anbo Wang1; Haixuan Yu1; Richard D. Sisson, Jr.1; 1Worcester Polytechnic Institute

RA602CA is an oxidation resistant high strength nickel based alloy that has been widely used for furnace fixtures in heat treatment processes. In this paper RA602CA and Aluminized RA602CA were selected to study their performance in an industrial carburization furnace for up to two years. In this report the microstructural development of both aluminized and unaluminized alloys during the prolonged exposure in the carburizing environment will be presented and discussed. Aluminizing can be used to increase the high temperature oxidation and carburization resistance of nickel based alloys. To experimentally investigate the thermal cycling resistance of the alumina on the alloys, cyclic oxidation experiments were conducted on the uncoated and aluminized RA602CA. Bend tests will be conducted to investigate the adherence of the alumina after the oxidation. These samples were characterized using optical and scanning electron microscopy, EBSD, and x-ray diffraction.

The Effects of Heating Rates on the Tempering of 4140 Steel

Xiaoqing Cai1; Richard Sisson1; 1Worcester Polytechnic Institute

Induction and furnace tempering can be used to achieve equivalent mechanical properties in quenched and tempered martensitic steels. Typically induction tempering takes place at higher temperatures for a short time while furnace tempering is conducted at lower temperatures for longer times. The great difference between these two tempering process is heating rates. This paper presents the experimental results of controlled furnace and induction tempering heat treatments with particular attention to microstructure, mechanical properties for AISI 4140 steel. It was found that the size, morphology, and number density of carbides present determine the mechanical properties and are strongly influenced by the heating rates. These results have widespread impact in several industrial applications relying on both furnace and induction quench and temper processes.

Enhancement to the modeling of the Carbon Concentration and Microhardness Profiles in Carburized Steel

Lei Zhang1; Richard Sisson1; 1WPI

The CHTE surface hardening simulation software CarbTool© have been enhanced to improve the accuracy of the simulation and to prediction the microstructure and microhardness profile after heat treatment. CarbTool© can be used for the prediction of both gas and low pressure carburizing process. The prediction has successfully predicted the carbon concentration profiles for gas carburizing process and mostly low pressure carburizing process. In some cases, the simulation tool may not work well with the low pressure carburizing process.An improved model for the process is proposed to more efficiently model the boundary condition. In the modeling, carbon potential and mass transfer coefficient are calculated and used.The mixture rule is used then to predict the hardness profiles. Experiments have been conducted to verify the simulation

Identification of the Important Material and Process Parameters that Control Distortion and Residual Stress in Heat Treatment

Haixuan Yu1; Yuan Lu1; Richard D. Sisson1; 1Worcester Polytechnic Institute

A series of computer simulation experiments, using DANTE had been conducted to determine the important material and process parameters that control distortion and residual stress. It was found that the Ms temperature of the steel, the yield strength of austenite as a function of temperature, the temperature dependence heat transfer coefficient of the quenching fluid, part orientation during quenching, immersion speed, quenchant temperature, austenitizing temperature and the part geometry are ranked based on their impact. In this paper, the result of these simulations will be presented and discussed.

Microstructure and Mechanical Properties of AISI4140 and Pyrowear53 after Gas and Liquid Quenching

Yuan Lu1; Haixuan Yu1; Richard D. Sisson, Jr.1; 1Worcester Polytechnic Institute

Gas quenching has the potential to replace liquid quenching for medium and high hardenability steels. Gas quenching can reduce distortion and is environmentally friendly. It was assumed that as long as the hardness are identical after quenching, the microstructure and mechanical properties are identical. This is not the case for medium hardenability steel, especially for high hardenability steel, when changing from oil quenching to gas quenching. In this paper, the microstructure and mechanical properties on AISI 4140 and Pyrowear 53 were compared after liquid and gas quenching. For AISI 4140, Charpy impact toughness increases when the cooling rate decreases during quenching. Water quenching and tempering provides the improved Charpy toughness. Austenite percentage and carbon content in austenite is proposed as the dominated mechanism. For P53, Charpy impact toughness decreases when the cooling rate decreases during quenching. Oil quenching and tempering provides the improved Charpy toughness.

Application of Computational Modeling to Trial and Error Minimization for Alloy Property Optimization

Derek Tsaknopoulos1; Danielle Cote1; Richard Sisson1; Victor Champagne2;1 Worcester Polytechnic Institute 2US Army Research Laboratory

Materials’ properties and qualification remains a substantial barrier to adoption of new alloy design and processing. While a detailed understanding of these materials are needed prior to utilization, the current widespread practice of trial and error leads to significant material development timelines. Focusing primarily on the determination of yield strength of aluminum alloys, a quantified strengthening model was developed using contributions from solid solution, grain size, dislocation, and precipitation strengthening mechanisms. This model makes use of the computed kinetic and thermodynamic outputs from the modeling software Thermo-Calc. The data from these models enable the ability to rapidly prototype a number of different situations, such as differences in processing methods, alloy compositions, and post-processing heat treatments. The effectiveness of this work is determined using thermal, optical, and mechanical characterization methods.