Au/Zn Contacts to rho-InP: Electrical and Metallurgical Characteristics and the Relationship Between Them

The metallurgical and electrical behavior of Au/Zn contacting metallization on p-type InP was investigated as a function of the Zn content in the metallization. It was found that ohmic behavior can be achieved with Zn concentrations as small as 0.05 atomic percent Zn. For Zn concentrations between 0.1 and 36 at. percent, the contact resistivity rho(sub c) was found to be independent of the Zn content. For low Zn concentrations the realization of ohmic behavior was found to require the growth of the compound Au2P3 at the metal-InP interface. The magnitude of rho(sub c) is shown to be very sensitive to the growth rate of the interfacial Au2P3 layer. The possibility of exploiting this sensitivity to provide low resistance contacts while avoiding the semiconductor structural damage that is normally attendant to contact formation is discussed

Tribology and Microstructure of PS212 with a Cr2O3 Seal Coat

PS212 is a plasma sprayed metal bonding chrome carbide coating with solid lubricant additives which has lubricating properties at temperatures up to about 900 deg C. The coating is diamond ground to achieve an acceptable tribological surface. But, as with many plasma spray coatings, PS212 is not fully-dense. In this study, a chromium oxide base seal coating is used in an attempt to seal any porosity that is open to the surface of the PS212 coating, and to study the effect of the sealant on the tribological properties of PS212. The results indicate that the seal coating reduces friction and wear when it is applied and then diamond ground leaving a thin layer of seal coating which fills in the surface pits of the PS212 coating

Oxygen Plasma Treatment and Deposition of CNx on a Fluorinated Polymer Matrix Composite for Improved Erosion Resistance

The use of polymer matrix composites in aerospace propulsion applications is currently limited by insufficient resistance to erosion by abrasive media. Erosion resistant coatings may provide necessary protection; however, adhesion to many high temperature polymer matrix composite (PMC) materials is poor. A low pressure oxygen plasma treatment process was developed to improve adhesion of CNx coatings to a carbon reinforced, fluorinated polymer matrix composite. Fullerene-like CNx was selected as an erosion resistant coating for its high hardness-to-elastic modulus ratio and elastic resilience which were expected to reduce erosion from media incident at different angles (normal or glancing) relative to the surface. In situ x-ray photoelectron spectroscopy was used to evaluate the effect of the plasma treatment on surface chemistry, and electron microscopy was used to identify changes in the surface morphology of the PMC substrate after plasma exposure. The fluorine concentration at the surface was significantly reduced and the carbon fibers were exposed after plasma treatment. CNx coatings were then deposited on oxygen treated PMC substrates. Qualitative tests demonstrated that plasma treatment improved coating adhesion resulting in an erosion resistance improvement of a factor of 2 compared to untreated coated composite substrates. The combination of PMC pretreatment and coating with CNx reduced the erosion rate by an order of magnitude for normally incident particles

Towards lube-free aluminum high pressure die casting using duplex AlCrN physical vapor deposition coatings

Aluminum high pressure castings (HPDC) were successfully produced on two simple but slightly different H13 steel dies that had been coated with AlCrN physical vapor deposition (PVD) coatings and without the use of conventionally-sprayed die lubricants. Over 200 lube-free (no lubricant) castings were produced in both of the dies. Temperature simulations of the dies matched well with thermal camera measurements taken during the trials, and helped explain the positions where small amounts of soldering and aluminum marks developed. Aluminum build-up on the die surfaces was observed as an intermittent phenomenon and did not lead to soldering. Due to the high gate velocities used in these trials, a large fraction of the AlCrN coating was washed out or cracked. No chemical reaction or intermetallic formation was observed on the analyzed surfaces, suggesting that build-up of aluminum on the die surface occurred by mechanical keying rather than by chemical soldering. A mechanistic model was developed to understand the correlation between surface roughness, wetting angle and HPDC pressure, in an attempt to explain why lube-free aluminum HPDC was possible for these simple die geometries, and to shed light on why it is more challenging for more complex die geometries. This study has demonstrated that lube-free aluminum die casting is possible by coating simple geometry dies with duplex AlCrN PVD coatings and suggests that lube-free castings might extend die life