CHARACTERISTIC OF INTERFACE BIMETAL ALUMINUM-COPPER FOR BIMETAL BUSHING PRODUCED BY CENTRIFUGAL CASTING

Bimetallic is a type of metal composite that combines two metals that form a metallurgical bond. The manufacture of bimetallic bushings by centrifugal casting has not been developed much. Recently, there is no recommendation yet for optimum temperature and speed of rotation to produce bimetallic bushings. The research was conducted to determine the rotation of the mold in centrifugal casting so as to produce a well-integrated interface. The materials used are aluminum and copper. Aluminum was melted at 750 °C, while copper was melted at 1200 °C. Molten metal was pouring alternately. First, aluminum was poured into the mold, and then after the aluminum temperature reached 400º C, copper was poured into the mold to form a bushing aluminum-copper bimetallic. The molten metal was poured into a rotating sand mold with a constant filling speed of about 0.15 kg s-1. The variations of the rotational speed of the mold were 250, 300, and 350 rpm. The result shows that the interface’s width increases as the mold rotation increases during the pouring process. Interface hardness and wear are increased compared to the base metal. Hence, centrifugal casting with 350 rpm is recommended for aluminum-copper bimetal bushing applications.

Interfacial Microstructure and Strength of Friction Welding of Steel Tube to Aluminium Tube Plate Using an External Tool

Joining of dissimilar materials is of increasing interest for a wide range of industrial applications like nuclear, thermal power. The automotive industry, in particular, views dissimilar materials joining as a gateway for the implementation of lightweight materials. Friction welding of tube to tube plate using an external tool is an innovative friction welding process and is capable of producing high quality leak proof weld joints. In the present study, friction welding of steel tube to commercial aluminum tube plate using an external tool with and without tube projection have been performed. The joints were evaluated by mechanical testing and metallurgical analysis. The results of bonding interface hardness and joint strength reveal that steel tube with projection are better than the steel tube without projection.

The Influences of Impact Interface, Muscle Activity, and Knee Angle on Impact Forces and Tibial and Femoral Accelerations Occurring after External Impacts

The purpose of this study was to quantify relative contributions of impact interface, muscle activity, and knee angle to the magnitudes of tibial and femoral accelerations occurring after external impacts. Impacts were initiated with a pneumatically driven impacter under the heels of four volunteers. Impact forces were quantified with a force sensor. Segmental accelerations were measured with bone mounted accelerometers. Experimental interventions were hard and soft shock interfaces, different knee angles (0°, 20°, 40° knee flexion), and muscular preactivation (0%, 30%, 60% of maximal voluntary contraction) of gastrocnemii, hamstrings, and quadriceps. Greater knee flexion led to lower impact forces and higher tibial accelerations. Increased muscular activation led to higher forces and lower tibial accelerations. The softer of the two shock interfaces under study reduced both parameters. The effects on accelerations and forces through the activation and knee angle changes were greater than the effect of interface variations. The hardness of the two shock interfaces explained less than 10% of the variance of accelerations and impact forces, whereas knee angle changes explained 25–29%, and preactivation changes explained 35–48% of the variances. It can be concluded that muscle force and knee joint angle have greater effects in comparison with interface hardness on the severity of shocks on the lower leg.

Properties and Fracture Resistance of Thin Polycrystalline Aluminum Films on Sapphire Substrates

We employed nanoindentation, continuous microscratch testing, and high resolution TEM to determine the effect of structure on the properties and resistance to fracture of thin polycrystalline aluminum films deposited onto single crystal sapphire substrates at 25°C and 250°C. These films had a nominal thickness of 90 nm and a grain size of 160 nm. The elastic and plastic properties were similar for both films. The elastic moduli superimposed, increasing from bulk aluminum values at the surface to sapphire values at the interface. Hardness values also superimposed, but were constant through the film thickness at a value between aluminum and sapphire. In contrast, susceptibility to fracture varied markedly between the films with the 25°C film exhibiting abrupt failure along the film-substrate interface while the 250'C film gave no indication of fracture in the film, along the interface, or in the substrate under the conditions tested.

Performance and Reliability of Ultrathin Oxynitride Gate Dielectrics Prepared using In-Situ Multiple Rapid Thermal Processing

ABSTRACTThe electrical characteristics of ultrathin oxynitride gate dielectrics prepared by in-situ multiple rapid thermal processing in reactive ambients (O2 and NH3) have been studied. Specifically, the conduction mechanism, charge trapping properties, time-dependent breakdown, and interface hardness in oxynitride films have been characterized as a function of both RTO and RTN processing parameters. In addition, N-channel MOSFET's have been fabricated using oxynitrides as gate dielectrics and their hot carier immunity has been examined and compared with devices with pure thermal oxides. Devices with superior electrical characteristics and reliability have been produced by optimizing RTO/RTN parameters.