PI: Anthony Rollett
University: Carnegie Mellon University
Carnegie Mellon University (CMU) and Hamilton Precision Metals (HPM), located near Lancaster, PA, and a subsidiary of Ametek, will collaborate on implementing advanced metallurgical practices for their products for the health care industry. This will build on the expertise in microstructural characterization and thermomechanical processing at CMU.
HPM processes Ti Grade 9 (Ti-3Al-2.5V) from plate to strip, which is used for manufacturing enclosures for medical implantable devices. Requirements include the ability to fabricate drawn enclosures with tight requirements for flatness and appearance. In particular, surfaces must pass a surface quality inspection prior to implantation. The most recent feedstock shipment to HPM had an adverse appearance that HPM’s customer terms “racing stripes,” i.e., a faintly ridged surface. Based on the industry’s experience for Ti plate to exhibit large prior beta grain size that causes anisotropic response to thermomechanical processing, HPM suspects that crystallographic texture is the cause. HPM’s customer has complained about this so a solution is sought. As this characteristic is new, it has not been incorporated into the specification. Neither HPM or its customer like the current surface appearance but they have been able to secure a deviation from the tier I manufacturer to use the strip.
HPM desires to understand whether process changes to rolling or annealing might be able to reduce the severity or eliminate the ridging appearance. It has been proposed that heat treating close to or above the Beta Transus temperature (1715 °F +/- 25 °F) might result in a microstructural change that favorably impacts this condition. HPM will cold roll the material to various reductions, i.e., sheet thicknesses, and anneal at various temperatures and line speeds. Carnegie-Mellon will support the project by characterizing the resulting strip via microstructural evaluation that includes orientation mapping to reveal crystallographic texture along with grain morphology.