The oxidation kinetics of ZrB 2 -30 vol% SiC were analyzed statistically with the goal of understanding the underlying mechanisms for observed variability. A box furnace was used to oxidize specimens for times between 30 s and 100 h at temperatures of 1300°C-1550°C in air. The specimens were characterized to determine weight change, scale thickness, and scale composition to quantify the oxidation behavior. Weight gain measurements of different specimens after 100 min of exposure showed differences of up to 2 mg/cm 2 for the same testing conditions where the average weight gain was 2.54 mg/ cm 2 . Variation of 30%-80% was observed in the average thickness of each layer of the oxide within a single specimen. Viscous glass flow was ruled out as a potential mechanism. Glass bubble formation was proposed as the main cause for oxidation kinetics variability.B. Fahrenholtz-contributing editor Manuscript No. 33581.

The composition of the borosilicate glass layer formed during oxidation of ZrB 2 -30 vol% SiC was determined to elucidate the extent of B 2 O 3 retention in the oxide during high-temperature oxidation. Oxidation was conducted in stagnant air at 1300°C, 1400°C, and 1500°C for times between 100 and 221 min. Specimens were characterized using mass change and scanning electron microscopy. After oxidation, the borosilicate glass layer was dissolved from the specimens sequentially with deionized H 2 O and HF acid, to analyze the glass composition using inductively coupled plasma optical emission spectrometry. It was found that the average B 2 O 3 content in the glass scale ranged from 23 to 47 mol%. Retained B 2 O 3 content in the bulk of the glass decreased with increasing temperature, confirming increased volatility with temperature. Boron depth profiles were also obtained in the near surface region using X-ray photoelectron spectroscopy and energy dispersive spectroscopy. The measured B concentrations were used to estimate the B 2 O 3 concentration profile and B diffusion coefficients in the borosilicate glass. Implications for the ZrB 2 -SiC oxidation process are discussed. 1 UES, Inc.; Dayton, OH 45432. †

The initial oxidation behavior of ZrB2–30 vol% SiC was analyzed with the goal of understanding any relationship to the variable oxidation performance observed at longer times. A box furnace was used to oxidize samples for times as short as 10 s and up to 100 min at 1500°C in air. The samples were characterized using mass change, scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy to explore the oxidation behavior. The presence of borosilicate glass and ZrO2 was observed on the surface at times as early as 10 s. Bubble formation in the borosilicate glass was observed after 30 s of oxidation and is attributed to uneven distribution of the glass. The impact of surface roughness on oxidation was also explored and found to be negligible for times greater than 30 s.

The formation of a porous SiC‐depleted region in ZrB2–SiC due to active oxidation at ultrahigh temperatures was characterized. The presence/absence of SiC depletion was determined at a series of temperatures (1300°C–1800°C) and times (5 min–100 h). At T < 1627°C, SiC depletion was not observed. Instead, the formation of a ZrO2 + C/borosilicate oxidation product layer sequence was observed above the ZrB2–SiC base material. At T ≥ 1627°C, SiC was depleted in the ZrB2 matrix below the ZrO2 and borosilicate oxidation products. The SiC depletion was attributed to active oxidation of SiC to form SiO(g). The transition between C formation in ZrO2 (T < 1627°C) and SiC depletion in ZrB2 (T ≥ 1627°C) is attributed to variation in the temperature dependence of thermodynamically favored product assemblage influenced by the local microstructural phase distribution. The growth kinetics of the SiC depletion region is consistent with a gas‐phase diffusion‐controlled process.

Abstract:The failure of a proximal humerus internal locking system (PHILOS) used in a pantalar arthrodesis was investigated in this paper. PHILOS constructs are hybrids using locking and non-locking screws. Both the plate and the screws used in the fusion were obtained for analysis. However, only the plate failure analysis is reported in this paper. The implant had failed in several pieces. Optical and scanning electron microscopic analyses were performed to characterize the failure mode(s) and fracture surface. The chemical composition and mechanical properties of the plate were determined and compared to controlling specifications to manufacture the devices. We found that equivalent tensile strength exceeded at the locations of high stress, axial, and angular displacement and matched the specification at the regions of lower stress/displacement. Such a region-wise change in mechanical properties with in vivo utilization has not been reported in the literature. Evidence of inclusions was qualitatively determined for the stainless steel 316L plate failing the specifications. Pitting corrosion, scratches, discoloration and debris were present on the plate. Fracture surface showed (1) multi-site corrosion damage within the screw holes forming a 45 • maximum shear force line for crack-linking, and (2) crack propagation perpendicular to the crack forming origin that may have formed due to the presence of inclusions. Fracture features such as beach marks and striations indicating that corrosion may have initiated the crack(s), which grew by fatigue over a period of time.In conclusion, the most likely mechanism of failure for the device was due to corrosion fatigue and lack of bony in-growth on the screws that may have caused loosening of the device causing deformity and pre-mature failure.

A polycrystalline 1.5% Ho: YAG fiber with a diameter of 31 µm was prepared. Surface roughness from grain boundary grooving was reduced by polishing, which decreased the fiber scattering coefficient from 76 m^-1 to 35 m^-1. Lasing tests were done on this fiber with a SF57 Schott glass cladding. Lasing was confirmed by spectrum narrowing with threshold pump power lower than 500 mW and a slope efficiency of 7%. To our knowledge, this is the first lasing demonstration from a small diameter polycrystalline ceramic fiber.

ZrB 2 -SiC is of high interest for Thermal Protection Systems (TPS) for future hypersonic vehicles. Both ZrB 2 and its oxidation product, ZrO 2 , possess high melting temperatures (T m =3245°C and 2715°C respectively) needed for this application. SiC is added to improve the oxidation resistance. However, the oxidation resistance of ZrB 2 -SiC at ultra-high temperatures is poor and the oxidation mechanisms are not well understood. The aim of this work was to perform a quantitative study of the oxidation behavior in order to improve life prediction.The oxidation behavior of ZrB 2 -30 vol% SiC was studied using two oxidation procedures. A box furnace was used to oxidize specimens for times between 30 seconds and 100 hours at temperatures of 1300°-1550°C in stagnant air. For ultra-high temperature testing, a resistive heating system was designed and built, which allowed oxidation at temperatures of 1300°-1800°C for times between 5 and 70 minutes in controlled oxygen atmospheres. Oxidation was quantified by measuring mass change and oxidation product layer thicknesses. A combination of scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectrometry, and time of flight secondary ion mass spectrometry was used to characterize the oxidation products.Two oxidation regimes were identified; 1) low temperature oxidation below 1627°C and 2) high temperature oxidation at and above 1627°C. Low temperature oxidation exhibited a twolayer oxide, which consisted of a borosilicate glass layer above a ZrO 2 +C layer. Key findings indicate that oxygen transport in both zirconia and borosilicate glass must be considered in modeling the low temperature oxidation behavior of ZrB 2 -30 vol% SiC. In addition composition and thickness variations of the borosilicate glass layer must also be considered. ivThe transition between the low and high temperature oxidation regimes is attributed to a change in the thermodynamically favored oxidation products, considering a locally SiC-rich microstructure. High temperature oxidation, T≥ 1627°C, resulted in formation of three oxidation product layers. A borosilicate glass layer was found above a layer with ZrO 2 and borosilicate glass. Beneath these was a porous layer of ZrB 2 resulting from SiC depletion due to active oxidation to SiO(g). Key findings indicate that the oxidation rate is much more rapid in this oxidation regime, that the SiC depletion layer growth is best explained by parabolic gas phase diffusion in the porous layer, and again, oxygen transport in both zirconia and borosilicate glass must be considered in modeling the high temperature oxidation behavior of ZrB 2 -30 vol% SiC.This work provided a quantitative analysis of the oxidation kinetics of ZrB 2 -30 vol% SiC.The thermodynamic and kinetic analyses of the two distinct oxidation regimes of ZrB 2 -30 vol% SiC enable improved life prediction.v

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