You are cordially invited to the latest double-header in our graduate student seminar series. Kuan Jiang will give a talk titled ” Effects of Heat Treatment on Microstructure and Wear Resistance of Stainless steels and superalloys” and Amir Ketabchi will talk about the Influence of Nanoscale Surface Modifications on the Fatigue Resistance of Medically Relevant Metals.
Date: Friday March 15th, 2013
Location: SITE G0103
The abstracts of both talks are given below. I look forward to seeing you all there!
Effects of Heat Treatment on Microstructure and Wear Resistance of Stainless steels and superalloys
Superalloys and stainless steels are two well-known families of high temperature materials with outstanding features including superb high temperature behavior, excellent wear/corrosion resistance, and astounding mechanical properties. They are commonly used in the severe environment to combat the synergetic attack of wear, corrosion and high temperature. The present research was aimed to characterize the influences of heat treatment on the microstructure, high temperature hardness and wear resistance of superalloys and stainless steels. Two cast cobalt-based superalloys and two wrought martensitic stainless steels were selected and applied an annealing heat treatment for this study. A Scanning Electron Microscope (SEM) with X-ray detection systems is utilized to investigate the microstructure developments of selected alloys after annealing treatment. Vickers hardness tests and pin-on-disc sliding wear tests were performed on as-received and heat-treated alloys at both room temperature and elevated temperatures up to 450oC. The research demonstrated that annealing treatment promoted the diffusion of carbides and alloying elements such as molybdenum and chromium, and contributed to the formation and precipitation of intermetallic compounds in cobalt-based superalloys. For stainless steels, the annealing heat treatment either resulted in the eutectoid transformation or altered the microstructure varied from their chemical compositions. The sliding wear test results indicated the annealing heat treatment influences the wear behavior of a superalloy or stainless steel through changing its harden strength, ability to resist fracture and oxidation behavior. However, the precipitation phenomenon on some alloys caused by heat treatment can harden the entire material meanwhile decrease its ability to resist fracture. The relationships between chemical composition, microstructure, hardness, wear resistance are also discussed in this research.
Influence of Nanoscale Surface Modifications on the Fatigue Resistance of Medically Relevant Metals
Metal implants are relatively effective but they still need significant improvements with respect to their capacity to secure rapid and long-lasting integration in tissues. To address these challenges, different strategies have been developed to directly affect the cellular events at the material-host tissue interface. Chemical treatments such as oxidative nanopatterning and anodization are very effective tools to endow medically relevant metals (in particular titanium and Ti6Al4V) with the ability to stimulate and guide cellular events. This remarkable capacity results from the creation of distinctive nanoporous surfaces. To date, only few studies focused on mechanical aspects to ensure that such chemical approaches do not weaken mechanical properties of treated metals. Nanoporous structures could in fact act as surface defects and/or stress-raisers responsible for initiating crack nucleation and lead to premature failure. To elucidate this aspect, we have assessed the effects of oxidative nanopatterning and anodization on the fatigue resistance of pure titanium and Ti6Al4V. In particular, we aimed at investigating the fatigue performance from both quantitative (i.e. S-N curves) and qualitative (i.e. morphological SEM analysis) perspectives. Results from our study highlight the importance of mechanical considerations in the development and evaluation of nanoscale surface treatments for metallic implants.