Compaction to full density is a means to deliver performance and precision without the distortion associated with sintering densification. High strain rate compaction using shock waves has been demonstrated as one means to attain full density in the green state. In the present study, variations in the compaction pressure are used to determine the conditions for attaining full density and these conditions are compared between high velocity and traditional die compaction technologies. A diminishing effect of compaction pressure on densification was observed. At the same compaction pressure the green density and hardness were lower using high velocity compaction. Sound velocity measurements in the powder show high velocity compaction did not generate a shock wave. Therefore, under subcritical compaction velocity conditions there is a higher green density from conventional compaction when compared using the same peak pressure.
A new method for anisotropic materials characterization based on phased-array ultrasonic transducers technology AIP Conf.ABSTRACT. Crack detection in unsintered, or green, powder metal parts has been of interest for decades with no commercial solution available. Traditional ultrasonic techniques using liquid couplant cannot be used with green parts since residue left behind from the couplant will degrade the final quality of the sintered part. In this paper, two couplant free techniques are presented for the inspection of green and sintered parts. The surface wave mediator technique uses point contact with a part to induce and receive Rayleigh surface waves which are sensitive to surface breaking cracks and density variations. The mediator tip can be shaped to effectively inspect both flat and curved geometries such as boreholes. Feasibility studies performed using ultrasonic electromagnetic acoustic transducers (EMATs) on both green and sintered parts have been successful in impinging ultrasonic energy into the parts for defect detection. Due to the low aspect ratio of many powder metal parts, ultrasonic guided waves can provide full part characterization. Shear horizontal waves were used to inspect the flange of a transmission part and torsional waves have been used to inspect the welded region of a sintered porous filter.
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