A quantitative evaluation, at the scanning electron microscopic (SEM) level, was made of the osteoconduction and osseointegration of Ti-6AI-4V implants with and without plasmasprayed hydroxyapatite coatings (HACs). By employing the Chinese Coin implant model in the lateral femora cortices of canines, different biological properties between HA-coated and uncoated Ti-6AI-4V implants could be compared in one specimen. After 4, 6 and 1 2 weeks, the implants with surrounding bone were removed and assessed histologically in undecalcified sections under SEM. The osteoconductivity and the ability of osseointegration of implants were histomorphometrically analysed from back-scattered electron images (BEIs) and represented in terms of the new bone healing index (NBHI) and apposition index (AI), respectively. Throughout all implant periods, the HA-coated Ti-6AI-4V implants revealed higher NBHI than the uncoated ones, it appearing that the HA-coated Ti-6AI-4V.implant was more osteoconductive than the Ti-6AI-4V was. For HA-coated implant, the evidence of direct bone-to-HAC contact was observed. However, at the bone/Ti-6AI-4V interface, there intervened a fibrous membrane without calcium content, indicating that the Ti-6AI-4V implant was not osseointegrated in the SEM field of view. The maximum value of AI was reached 6 weeks after implantation for HA-coated implant, implying that the HAC had a stimulating influence on bone apposition within 6 weeks of healing. The signs of partial dissolution of HACs within the remodelling canals were evident at the HAC-bone interface 1 2 weeks after implantation, accounting for the slight decrease in NBHI and the obvious decrease in AI for HAC implant.

No abstract

No abstract

Duplex Zr02-8 wt % Y2O3/Ni-22Cr-1OAI-1Y thermal barrier coatings (TBCs) on Mar-M247 superalloy were tested under different operating conditions within the temperature range 1000" to 1150°C. Results of experiments in this study show that oxidation of bond coatings is the dominant TBC degradation mechanism whereas the operationally induced stresses exert a conjugate effect. The mechanisms of sintering and phase transformation of top coatings do not contribute to failure of TBCs within the temperature range studied. NiO and Ni(Cr,Al)204 grown on the surfaces of the bond coatings seem to accelerate spalling of the top coatings along a top coating/ bond coating out-grown oxide interface. However, it is also concluded that the lifetime of TBCs is not directly related to a critical specific weight gain under thermal cycling conditions. [

Tungsten carbide coatings applied by the plasma spray process have been widely used in wear applications. In the W–C–Co ternary system, tungsten carbide can either be present as WC or W2C. Frequently WC transforms into W2C during the plasma spray process. In this study, tungsten carbide/17% cobalt coatings were applied by both the air plasma and the vacuum plasma spray processes using different power levels and plasma gases. The W2C phase was found by X-ray diffraction techniques in the air plasma sprayed coatings. Decarburizing of the WC in the presence of the oxygen took place in the plasma. In this study air plasma sprayed coating hardness and microstructure are superior to those of the vacuum plasma sprayed ones. However the vacuum plasma coatings were found to be more wear and impact resistance than the air plasma coatings. This performance difference may be attributed to the presence of hard and brittle W2C phase in the air plasma sprayed tungsten carbide coatings.