adam l. pilchak

papers / presentations
about me:
 I'm a grad student at The Ohio State University studying Materials Science and Engineering with emphasis on physical metallurgy of titanium alloys.
Current abstracts that have been submitted from projects that I have been involved:

MS&T 2006 to be held in Cincinnatti, OH
October 15 - 19, 2006

The Effect of Friction Stir Processing on the Microstructure of an alpha/beta Ti Alloy
Adam Pilchak, Paul Pavka, Mary Juhas & Jim Williams
Materials Science & Engineering
The Ohio State University
Columbus, OH 43210

Titanium alloy castings have grown in popularity because they are a cost-effective way of making complex shapes. However, the relatively low fatigue crack initiation resistance of the coarse as-cast lamellar microstructure is a limitation. Friction stir processing (FSP) has been used to modify the as-cast microstructure of Ti-6Al-4V. We have found that FSP creates a very fine (1-2 m diameter) equiaxed microstructure. Using a variety of characterization techniques and test methods we have examined the effect of this very fine-grained structure on deformation and fatigue behavior. This talk will describe the microstructural changes induced by FSP and discuss the mechanism by which these changes occur. It also will illustrate the effects of these changes on properties. This microstructural evolution will also occur in friction stir welding of Ti alloys and the effect of this on weld performance will be discussed. This work is supported by the Office of Naval Research.


Particle Size Reduction of LAST Thermoelectrics Powders by Planetary Ball Milling
 Fei Ren, Adam Pilchak, Stacey Schroeder, Jason Johnson, Eldon Case, Edward Timm, Harold Schock
Department of Chemical Engineering and Materials Science
Michigan State University
East Lansing, MI 48224

The conversion of waste heat into electricity for automobile or truck applications requires thermoelectric materials with high energy conversion efficiency and good mechanical integrity. However, cast thermoelectric materials typically have large grain size and poor mechanical properties. Mechanical milling techniques can produce micron-sized powder particles that are essential to obtain dense specimens with small grain size. A planetary ball milling study was performed on a LAST (lead-antimony-silver-tellurium) cast material. The mean powder particle size was found to decrease exponentially with increasing milling time and particle size as small as 5 microns was achieved after 7 hours of milling. Particle shapes were elongated at short milling times and became more equiaxed as the milling time increased. The implications for the particle size and shape evolution on powder processing will be discussed.

TMS 2007 to be held in Orlando, FL
February 25 - March 1, 2007


The Relationship Between Friction Stir Process (FSP) Parameters and Microstructure of Investment Cast Ti-6Al-4V
Adam Pilchak, Tim Li*, Jim Fisher*, Mary Juhas, & Jim Williams
Materials Science & Engineering
The Ohio State University
Columbus, OH 43210

*Edison Welding Institute
Columbus, OH 43210

Titanium alloy castings have a coarse, fully lamellar microstructure which results in lower yield strength and high cycle (HCF) fatigue life than comparable wrought products. A study of FSP has demonstrated the microstructure at the surface can be modified to eliminate the coarse as-cast microstructure. FSP can transform the as-cast microstructure into a range of microstructures, all of which are finer than the as-cast structure. These range from very fine (1 - 2 micron diameter) equiaxed microstructures to lamellar structures with 20 - 40 micron prior grains. Such fine-grained equiaxed structures are difficult to produce in wrought products. We have used a variety of characterization techniques to investigate these microstructural changes. The changes will be illustrated and discussed in terms of the FSP parameters. The mechanism for the observed microstructure evolution will be described. This work is supported by the Office of Naval Research under contract N00014-06-1-0089.

Ti-2007, World Titanium Conference to be held in Kyoto, Japan
June 3 - 7, 2007


The Effect of Friction Stir Processing on Microstructure and Properties of Investment Cast Ti-6Al-4V
A.L. Pilchak, M.C. Juhas and J.C. Williams
The Ohio State University
116 W. 19th Avenue        Columbus, OH 43210
ph. +16142927251        fax: +16142924668

Investment cast titanium components are becoming increasingly common in the aerospace industry due to the ability to produce large, complex, one-piece components that were previously fabricated by mechanically fastening multiple pieces together. The fabricated components are labor intensive and the fastener holes are stress concentrators and prime sites for fatigue crack initiation. The castings are typically hot isostatically pressed (HIP) to close internal porosity, but have a coarse, fully lamellar structure which has low resistance to fatigue crack initiation but excellent fatigue crack growth. The as-cast + HIP material exhibited 1 to 1.5 mm prior ? grains containing a fully lamellar ? + ? microstructure consistent with slow cooling from above the ? transus. Friction stir processing (FSP) was used to locally modify the microstructure of an investment cast Ti-6Al-4V plate. FSP converted the as-cast microstructure to fine (1 to 2 µm) equiaxed ? grains on the surface of the plate. Using micropillars created in a FIB, it was found that the fine grained structure has about 35% higher compressive yield stress. In wrought products, higher strength conditions are more are more resistant to fatigue crack initiation while the coarse lamellar microstructure in the base material has better fatigue crack growth resistance. In combination, these two microstructures can increase the fatigue life of titanium alloy castings by increasing the number of cycles prior to crack initiation while retaining the same low crack rates. In the current study, high cycle fatigue testing of investment cast Ti-6Al-4V was performed on four-point bend specimens. Results of the effect of FSP microstructure on fatigue strength will be presented. The microstructural evolution including the mechanism of grain refinement during FSP will also be discussed. The relationship between process parameters and FSP microstructure also has been examined in detail and will be described.