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Biomedical subjects

H L Fraser

Publications and source records attributed to H L Fraser.

6 recordsLinked to original sources
PubMed2006

A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials.

The new generation of metallic biomaterials for prosthesis implantation (orthopedic and dental) typically have a Ti base with fully biocompatible alloying additions such as Nb, Ta, Zr, Mo, Fe and Sn. While the binary Ti-Ta and the ternary Ti-Nb-Ta systems are promising, the large composition space afforded by these systems offers tremendous scope in terms of alloy design via optimization of alloy composition and thermomechanical treatment. In the present paper a novel combinatorial approach has been developed for rapidly exploring the microstructural evolution and microstructure-microhardness (or elastic modulus) relationships in these systems. Using directed laser deposition, compositionally graded alloy samples have been fabricated and subsequently heat-treated to affect different microstructures in terms of the volume fraction and distribution of the alpha phase in the beta matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these graded samples, and the resulting data have been used to develop relationships between the composition, microstructure and mechanical properties. Such rapid combinatorial assessments can be very useful in optimizing not only the alloy composition but also the desired microstructure for achieving the best combination of properties for specific orthopedic or dental applications.

Alloys↗
PubMed2006

Laser-deposited Ti-Nb-Zr-Ta orthopedic alloys.

The complex quaternary Ti-35Nb-7Zr-5Ta orthopedic alloy has been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, and tantalum powders, using the laser engineered net-shaping (LENStrade mark) process. In the as laser-deposited form, these alloys exhibit a substantially higher tensile strength as compared with more conventionally processed counterparts of similar composition, while maintaining excellent ductility and a low modulus. Furthermore, the as-deposited alloys appear to exhibit a <001> texture, with a substantially large number of grains of the beta phase aligning one of their <001> axes nearly normal to the substrate or parallel to the growth direction. The microstructure of the as-deposited as well as tensile-tested alloys have been characterized in detail using scanning electron microscopy (SEM), orientation microscopy (OM), and transmission electron microscopy (TEM). Formation of a high density of shear bands, possibly arising from slip localization due to precipitates of the omega phase in the beta matrix, is clearly evident in the tensile-tested sample. The enhanced tensile strength and low modulus in these laser-deposited alloys coupled with the ability to form near-net shape components makes LENS an attractive processing technology for orthopedic implants.

Alloys↗
PubMed2005

Comparison of microstructural evolution in Ti-Mo-Zr-Fe and Ti-15Mo biocompatible alloys.

The microstructural evolution and attendant strengthening mechanisms in two biocompatible alloy systems, the binary Ti-15Mo and the quaternary Ti-13Mo-7Zr-3Fe (TMZF), have been compared and contrasted in this paper. In the homogenized condition, while the Ti-15Mo alloy exhibited a single phase microstructure consisting of large beta grains, the TMZF alloy exhibited a microstructure consisting primarily of a beta matrix with grain boundary alpha precipitates and a low volume fraction of intra-granular alpha precipitates. On ageing the homogenized alloys at 600 degrees C for 4 h, both alloys exhibited the precipitation of refined scale secondary alpha precipitates homogeneously in the beta matrix. However, while the hardness of the TMZF alloy marginally increased, that of the Ti-15Mo alloy decreased substantially as a result of the ageing treatment. In order to understand this difference in the mechanical properties after ageing, TEM studies have been carried out on both alloys in the homogenized and homogenized plus aged conditions. The results indicate that the omega precipitates dissolve on ageing in case of the Ti-15Mo alloy, consequently leading to a substantial decrease in the hardness. In contrast, the omega precipitates do not dissolve on ageing in the TMZF alloy and the precipitation of the fine scale secondary alpha leads to increased hardness.

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PubMed2004

Some aspects of atom probe specimen preparation and analysis of thin film materials.

Some of the factors in the preparation of atom probe specimens of metallic multilayer thin films have been investigated. A series of Ti/Nb multilayer films were sputtered deposited on n-doped Si [001] substrates with either 5 or 0.05Omega cm resistivity. Each wafer was pre-fabricated into a series of 5 microm x 5 microm x approximately 80 microm island posts by photolithography and reactive ion etching. Once the film was grown on the wafer, a Si post was mounted to either a tungsten or stainless steel fine tip needle that was mechanically crimped to a Cu tube for handling. The specimen was then loaded into a Focus Ion Beam instrument where a sacrificial Pt cap was in situ deposited onto the surface of the film and subsequently annularly ion milled into the appropriate geometry. The Pt cap was found to be an effective method in reducing Ga ion damage and implantation into the film during milling. The multilayers deposited on the high resistivity Si exhibited uncontrolled field evaporation which lead to high mass tails in the mass spectra, a reduction in the mass resolution, high background noise, propensity for "flash-failure", and a variation in the apparent layer thickness as the experiment elapsed in time. The multilayers deposited on lower resistivity Si did not suffer from these artifacts.

Mass Spectrometry↗
PubMed1990

Moiré fringe analysis of small precipitates in melt-spun titanium-silicon alloys.

Oxygen-contaminated, melt-spun, binary Ti-Si alloys have been examined by using transmission electron microscopy. The microstructure of alloys in the range of 4 to 10% Si (by weight) are cellular and consist primarily of alpha-Ti and the silicide Ti5Si3. Contained only within the Ti5Si3 regions are small, approximately spherical particles which are less than or equal to 10 nm in diameter. Due to their small size, the crystal structure of these particles could not be determined by using conventional diffraction techniques such as Selected Area or Convergent Beam Diffraction. By conducting a number of tilting experiments and observing the moiré fringe patterns produced when various matrix Ti5Si3 planes were used to image the sample, the crystal structure of the particles and the orientation relationship which exists between them and the matrix were deduced. The unknown particles, termed the Z phase, were found to be hexagonal with slightly different lattice parameters from the matrix Ti5Si3. Their relationship with the matrix was such that they appeared to be totally coherent. This may indicate that Z is an oxide based on the intermetallic Ti5Si3.

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