Papers by Author: William H. Peter

Abstract: Utilization of titanium components made by powder metallurgy methods has had limited acceptance largely due to the high cost of titanium (Ti) powder. There has been renewed interest in lower cost economical powders and several Ti reduction methods that produce a particulate product show promise. This talk summarizes work done at Oak Ridge National Laboratory to consolidate these economical powders into mill products. Press and sinter consolidation, hot isostatic pressing (HIP) and direct roll consolidation to make sheet have been explored. The characteristics of the consolidated products will be described as a function of the consolidation parameters.

Abstract: This work used in-situ and ex-situ techniques to investigate the pressing and sintering processes of commercially pure (CP) Ti powder made by the Armstrong process. The objective is to simulate the actual manufacturing process of near net shape Ti components. Ti powders were uniaxially pre-pressed at designated pressures up to 100 ksi to form disk samples with different theoretical densities. Compression tests were performed in an SEM at different temperatures to obtain the mechanical properties and deformation behavior of these samples. Ex-situ technique was used to track the powder deformation process of disk samples from low pressure to high pressure. In-situ sintering was also performed in an SEM to record the morphology change of the porosities on the sample surface during the sintering process. The results will provide valuable information for optimizing the manufacturing process of high-density near net shape Ti components.

Abstract: This paper summarizes our recent efforts to develop the manufacturing technologies of consolidated net-shape components by using new low-cost commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy powders made by the Armstrong process. Fabrication processes of net shape/ near net shape components, such as uniaxial die-pressing, cold isostatic pressing (CIP), sintering, roll compaction and stamping, have been evaluated. The press-and-sinter processing of the powders were systematically investigated in terms of theoretical density and microstructure as a function of time, pressure, and temperature. Up to 96.4% theoretical density has been achieved with the press-and-sinter technology. Tensile properties of the consolidated samples exhibit good ductility as well as equivalent yield/ultimate tensile strengths to those of fully consolidate materials, even with the presence of a certain amount of porosity. A consolidation model is also under development to interpret the powder deformation during processing. Net shape components made of the Armstrong powder can successfully be fabricated with clearer surface details by using press-and-sinter processing.

Abstract: Recent interest in bulk-metallic glasses (BMGs) has led to the development of amorphous alloys designed for structural applications in various fields as aircraft frames, rotating equipment, automobiles, and medical implants. Although the mechanical behavior of BMGs is being studied extensively, little attention has been paid to their fatigue behavior. Moreover, early fatigue characteristics have exhibited contradictory results. In the current research, uniaxial tension-tension fatigue experiments were performed on notched Zr52.5Cu17.9Al10Ni14.6Ti5 button-head fatigue specimens with various surface finishes. The fatigue studies were designed to better understand the influence of the average surface roughness and/or critical surface defects on the fatigue behavior of glassy alloys. It was hypothesized that geometric surface flaws would lower the observed life of a BMG sample by shortening the crack initiation phase and providing local stress concentrators. The current studies of surface conditions indicate that fatigue-endurance limits are greatly impacted by the average surface roughness with possible reductions of greater than fifty percent.