EXPERIMENTAL INVESTIGATION ON STRESS AND DIE-WALL FRICTIONAL CHARACTERISTICS OF METAL POWDER DURING HIGH-VELOCITY COMPACTION

In this study, to evaluate the change in the stress and die-wall frictional characteristics during high-velocity compaction (HVC), a metal powder was subjected to HVC with a heavy hammer based on the stress-testing technology and Janssen-Walker model. The changes in the green density, stress characteristics and coefficients of friction at different impact heights were investigated. The density of green compacts increased with the increase in the impact height. The stress in the upper and lower punches and the die wall showed repeated loading and unloading. The coefficient of friction of the die wall underwent three stages and was related to powder densification. As the height position along the side wall was increased, the coefficient of friction increased gradually. With an increased impact height, the coefficient of friction increased significantly in the incomplete-molding stage but remained constant in the complete-molding stage. This work expands the theoretical basis of densification processing of a metal powder during HVC.

Effects of Sintering Temperature on Densification, Microstructure and Mechanical Properties of Al-Based Alloy by High-Velocity Compaction

This present work investigates the effects of sintering temperature on densification, mechanical properties and microstructure of Al-based alloy pressed by high-velocity compaction. The green samples were heated under the flow of high pure (99.99 wt%) N2. The heating rate was 4 °C/min before 315 °C. For reducing the residual stress, the samples were isothermally held for one h. Then, the specimens were respectively heated at the rate of 10 °C/min to the temperature between 540 °C and 700 °C, held for one h, and then furnace-cooled to the room temperature. Results indicate that when the sintered temperature was 640 °C, both the sintered density and mechanical properties was optimum. Differential Scanning Calorimetry, X-ray diffraction of sintered samples, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and Transmission Electron Microscope were used to analyse the microstructure and phases.

Effects of Compaction Velocity on the Sinterability of Al-Fe-Cr-Ti PM Alloy

In this research, the effects of the compaction velocity on the sinterability of the Al–Fe–Cr–Ti powder metallurgy (PM) alloy by high velocity compaction were investigated. The Al–Fe–Cr–Ti alloy powder was compacted with different velocities by high velocity compaction and then sintered under a flow of high pure (99.999 wt%) nitrogen gas. Results indicated that both the sintered density and mechanical properties increased with increasing compaction velocity. By increasing the compaction velocity, the shrinkage of the sintered samples decreased. A maximum sintered density of 2.85 gcm−3 (relative density is 98%) was obtained when the compaction velocity was 9.4 ms−1. The radial and axial shrinkage were controlled to less than 1% at a compaction velocity of 9.4 ms−1. At a compaction velocity of 9.4 ms−1, sintered compacts with an ultimate tensile strength of 222 MPa and a yield strength of 160 MPa were achieved. The maximum elongation was observed to be 2.6%. The enhanced tensile properties of the Al–Fe–Cr–Ti alloy were mainly due to particle boundary strengthening.