The crystal structure of sputter deposited chromium thin films on Coming 7059 glass, polytetrafluoroethylene, and cold rolled (110) oriented low carbon steel α-Fe substrates was investigated as a function of O and C incorporation into the growing Cr film. The as-deposited crystal structure of the films was found by X-ray diffraction to be either highly oriented (110) BCC α-Cr or (200) oriented A-15 δ-Cr. Chemical analysis of the films by Auger electron spectroscopy determined that the δ-Cr phase formed when the combined O and C impurity concentration in the film was ~15-30 at%. At total impurity concentrations above ~30 at.% or below ~10 at.% standard BCC α-Cr formed. The crystal structure of the films was not influenced by the substrate material. X-ray photoelectron spectroscopy of the Cr 2p1/2-2p3/2 orbitals indicated that the dominate binding state of both the BCC α-Cr and A-15 δ-Cr films was characteristic of elemental Cr. Vacuum annealing of the A-15 δ-Cr films at 500°C for one hour transformed the crystal structure into BCC α-Cr without a measurable change in chemical composition. The incorporation of O and C into the growing Cr film is believed to impurity stabilize the A-15 structure and favor its formation over the BCC structure.

CuAgZr alloy is a variant of the CuAg alloy that is developed for high strength and high conductivity applications. Its strengthening is accomplished mainly by the precipitation of Ag precipitates, which tend to align on {111} planes in the Cu matrix. This alignment has been reported to be caused by stacking faults on {111} planes. Contrary to these reports, this research presents evidence for Ag precipitates formation on {111} planes due to the minimization of elastic energy. The Ag precipitates were formed by clustering of Ag atoms while maintaining the fcc crystal structure of the matrix. They have faceted {111} interfaces with the matrix. The thickening of precipitates appears to be by the ledge growth mechanism, which is resulted in by misfit dislocation networks on the interface.

The ability to make components from copper and copper alloys via additive manufacturing is spurring a range of novel applications. Although the high thermal conductivity of copper presents challenges for direct AM processes, fully dense copper components with complex geometries have been demonstrated. Of particular interest is the ability to use AM methods to fabricate internal cooling channels and mesh structures to optimize thermal management. This article describes feasibility studies to evaluate AM processing of copper parts.

Niobium is used to fabricate superconducting radio frequency accelerator modules because of its high critical temperature, high critical magnetic field, and easy formability. Recent experiments have shown a very significant improvement in performance (over 100%) after a high‐temperature bake at 1400 °C for 3 h. SIMS analysis of this material showed the oxygen profile was significantly deeper than the native oxide with a shape that is indicative of diffusion. Positive secondary ion mass spectra showed the presence of Ti with a depth profile similar to that of O. It is suspected that Ti is associated with the performance improvement. The source of Ti contamination in the anneal furnace has been identified, and a new furnace was constructed without Ti. Initial results from the new furnace do not show the yield improvement. Further analyses should determine the relationship of Ti to cavity performance. Copyright © 2014 John Wiley & Sons, Ltd.

Interstitial impurities such as C, N, O and H on the Nb surface play a key role in the efficiency of superconducting radio frequency (SRF) cavities for particle accelerators. Thus, it is important to understand the behaviour of these interstitial impurities with respect to grain boundaries. The large single crystal grains in large grain Nb make it possible to select bicrystal samples that have a well defined grain boundary. In this work, Dynamic SIMS was used to analyze two Nb bicrystal samples, one of them heat treated and the other chemically treated by buffered chemical polishing (control). H levels were found to be higher for the control sample and a difference in the H intensity and sputtering rate was also observed across the grain boundary for both samples. Transmission Electron Microscopy (TEM) was used to study the bicrystal interface and the surface oxide layer. The interface showed no discontinuity and the oxide layer was uniform across the grain boundary for both samples. TOF-SIMS imaging was also performed to analyze the distribution of the impurities across the grain boundary in both samples. C was observed to be segregated along the grain boundary for the heat treated sample, while H and O showed a difference in signal intensity across the grain boundary. Crystal orientation appears to have an important role in the observed sputtering rate and impurity ion signal differences, both across the grain boundary and between samples.

Superconducting Radio Frequency (SRF) cavities provide enhanced efficiency and reduced energy utilization in present day particle accelerators. Niobium (Nb) is the material of choice for these cavities due to its high critical temperature and critical magnetic field. In order to understand why certain treatments, especially a low temperature bake, improve performance, it is important to study Nb surface characteristics and identify elemental contamination that can affect the performance of the cavity. H. C, O, and N are of interest because they are interstitial impurities in Nb. In earlier work, SIMS analysis using a CAMECA IMS-6F with Cs+ primary beam showed that C and N were probably not significant factors impacting performance but there was a very high level of H in the Nb. Ion implants of C, N, O, and D into Nb provided quantification of C, N,O and indicated that D is very mobile in the Nb. Further analyses showed that heat treated Nb has lower levels of surface H than non heat treated Nb and subsequent removal of surface oxide by etching causes intake of H in a heat treated Nb sample. This result helps confirm the role of surface oxide as a hydrogen barrier. To further understand the oxide, Nb samples were anodized to obtain a thicker surface oxide and H and D were implanted into this oxide to check for the appearance of implant peaks. SIMS depth profile analyses were carried out and confirmed the presence of the implant shape for these elements in the oxide. Relative Sensitivity Factor (RSFs) could then be calculated for quantification of H in the oxide. Since the Nb matrix signal showed little change from the oxide to the substrate, the same RSF was used to estimate the H concentration in the Nb at 2x10(22) atoms/cm(3) (approximately 40% mole fraction H).

Superconducting Radio Frequency (SRF) cavities provide enhanced efficiency and reduced energy consumption in present‐day particle accelerators. Niobium is the material of choice for SRF cavities due to its high critical temperature and critical magnetic field. In order to understand why certain treatments, especially a low temperature bake, improve performance, it is important to study Nb surface characteristics and identify elemental contaminants which may affect the performance of the cavity. 1 Initial studies using SIMS and Focused Ion Beam (FIB) prepared specimens for Transmission Electron Microscopy (TEM) have helped to characterize the Nb surface and measure the surface oxide layer thickness. 2 C, N and O are of particular interest as interstitial contaminants and earlier studies suggested very high H concentration. In the present study, ion implants of C, N, O and deuterium ( D ) in Nb and Si were analyzed using SIMS. D was implanted to characterize H while avoiding interference from the high H background. The D implant was easily detectable in Si, but showed a constant value and no implant shape in Nb. This result implies either that D (and by implication, hydrogen) has a high mobility in Nb, or that there is movement of D due to the primary ion beam. Nevertheless, C, N, and O could be quantified using the ion implants. Depth profiles of polycrystalline and single crystal Nb samples were also obtained. While both types of Nb samples contained low C concentration, the single crystal Nb samples showed higher N and O content. Copyright © 2010 John Wiley & Sons, Ltd.

Precipitation-strengthened Cu-based alloys have limited use as structural materials at high temperatures due to precipitate coarsening and strength loss. We have recently shown that Curefractory metal alloys produced by various physical vapor deposition methods have stable, nanocrystalline microstructures and maintain their strength properties even when annealed at temperatures as high as 900 C for up to 100 hours. This paper presents discussions of how these alloys are processed and the resulting microstructures. X-ray and electron microscopy results will be presented to document the phase transformations that occur in these alloys and result in such exceptionally stable microstructures.

Criticisms of reports that ferrite laths have a sessile interfacial structure are refuted. A local lattice correspondence, achieved across coherent regions between interfacial defects, suffices to produce surface reliefs and martensitic crystallography [Prog. Mater. Sci. 42 (1997) 101]. However, formation of tent-shaped surface reliefs by monocrystalline laths/plates is inconsistent with martensitic growth.

Calcium phosphate (CaP) coatings, from 40,000 to 200,000 nm thick, on titanium and titanium alloy substrates, were produced using radio frequency (RF) sputtering. Such coatings on dental implants have the potential for improving initial bone ingrowth rates. The success of these coatings may allow the movement from two stage implant systems to single stage implant systems, significantly reducing the time required for healing and fixture placement. Glass source materials were developed for the RF sputtering facility and the resultant coatings were characterized and compared to coatings sputtered from a conventional plasma sprayed hydroxyapatite (HA) source material. The coatings were characterized according to their chemistry, crystalline orientation, and residual strain.

Zirconia coatings were produced by reactive d.c. magnetron sputter deposition using a system with multiple sputter sources and a biased substrate stage. Crystal structure and phase stability of the coatings were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tetragonal zirconia with either a random orientation or a highly (111) preferred orientation was deposited when a substrate bias was applied, whereas coatings grown with no substrate bias had the equilibrium monoclinic structure. It was revealed that bias sputtering effectively decreased crystallite size in the as-deposited coatings, which resulted in room temperature stabilization of the metastable tetragonal phase. XRD analysis of annealed coatings showed that the volume fraction and stability of the tetragonal phase was strongly dependent on substrate bias and annealing temperature.

The success of calcium phosphate (CaP) coatings used to accelerate initial bone growth onto dental implants can vary depending on the CaP phases present in the coating. In this study, the effect of CaP coating crystal structure and morphology on dissolution rates was investigated. RF magnetron-sputtered CaP coatings (NTC) were compared to a less strained coating (HTC) obtained from heat treatment of sputtered samples at 550 degrees C. Coating strain differences were apparent in XRD spectra where hydroxyapatite-like planes shifted by 0.5 degrees 2theta and 0.05 degrees 2theta for the NTC and HTC coatings, respectively. HTC XRD peak widths were broader than NTC peak widths, indicating smaller crystals or grain sizes. These differences in grain size were corroborated by imaging with scanning probe microscopy. NTC coatings dissolved at a 300% faster rate than HTC coatings. A major factor contributing to this kinetic effect was the level of strain in both coatings. These results suggest an alternate design for CaP coatings can be obtained through the manipulation of coating strain. Using this approach, delivery of different ionic gradients from CaP coatings to surrounding tissue environments can be obtained from surfaces having similar chemistries.

Zirconia coatings were produced by reactive dc magnetron sputter deposition, using a system with multiple sputter sources and a biased substrate stage. Tetragonal zirconia with either a random orientation or a highly (111) preferred orientation was formed by applying a substrate bias. Coating grown with no substrate bias had the equilibrium monoclinic structure. X-ray diffraction and transmission electron microscopy analyses revealed that bias sputtering could effectively decrease crystalline size in the as-deposited coating, which resulted in room-temperature stabilization of the tetragonal phase. The fraction of tetragonal phase, the desired phase for transformation-toughening behavior, was strongly dependent on the substrate bias and post-deposition annealing temperature.

Yttria‐stabilized zirconia (YSZ) coatings were produced by reactively cosputtering metallic zirconium and yttrium targets in an argon and oxygen plasma using a system with multiple magnetron sputtering sources. Coating crystal structure and phase stability, as functions of Y 2 O 3 content, substrate bias, and annealing temperature, were investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Results demonstrated that highly (111)‐oriented tetragonal and cubic zirconia structures were formed in 2 and 4.5 mol% Y 2 O 3 coatings, respectively, when the coatings were grown with an applied substrate bias. Conversely, coatings deposited with no substrate bias had random tetragonal and cubic structures. XRD analysis of annealed coatings showed that the cubic zirconia in 4.5 mol% Y 2 O 3 coatings exhibited structural stability at temperatures up to 1200°C. Transformation of the tetragonal to monoclinic phase occurred in 2 mol% Y 2 O 3 coating during high‐temperature annealing, with the fraction of transformation dependent on bias potential and annealing temperature.

The effects of laser-shock processing (LSP) on the microstructure, microhardness, and residual stress of low carbon steel were studied. Laser-shock processing was performed using a Nd:glass phosphate laser with≈600 ps pulse width and up to 120 J pulse energy at power densities above 1012 W cm−2. The effects of shot peening were also studied for comparison. Laser-shock induced plastic deformation caused the surface to be recessed by≈1.5 μm and resulted in extensive formation of dislocations. Surface hardness increased by up to 80% after the LSP. The microstructure and mechanical properties were altered up to≈100 μm in depth. The LSP strengthening effect on low carbon steel was attributed to the presence of a high dislocation density. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than did LSP.

The microstructure and properties of Cu-C pseudoalloy films prepared by R.F. magnetron sputtering have been investigated. As Cu and C are mutually immiscible, nonequilibrium supersaturated solid solutions of C in Cu with nanocrystalline microstructures were observed in as-deposited films. Upon heating of the films, three major transition events took place. Recovery occurred at ∼280 to 300 °C, while at ∼400 °C, crystallites started to growth and coalescence, due to the release of strain energies stored during deposition. Annealing at above 600 °C led to the occurrence of grain growth and altered the microstructure considerably. Although attempts have been made in this study, a possible annealing-induced phase separation could not be unambiguously identified. Yet, the fact of low twin densities and fine grain structures observed in the annealed films suggests that the extensive grain growth was impeded by the presence of carbon. Resistivity and hardness properties correlated well with the film microstructure and were governed by the impurity effect of carbon. Low-carbon Cu-C films yielded relatively low resistivity, attributable to the improved film microstructure. Hardness results indicated the strengthening of films was mainly due to fine structure, presence of carbon, and grain refinement by annealing twins.