The structure-property relationships of powder processed Fe-Al-Si alloys

Iron-aluminum alloys have been extensively evaluated as semi-continuous product such as sheet and bar, but have not been evaluated by net shape PN processing techniques such as metal injection molding. The alloy compositions of iron-aluminum alloys have been optimized for room temperature ductility, but have limited high temperature strength. Hot extruded powder alloys in the Fe-Al-Si system have developed impressive mechanical properties, but the effects of sintering on mechanical properties have not been explored. This investigation evaluated three powder processed Fe-Al-Si alloys: Fe-15Al, Fe-15Al-2.8Si, Fe-15Al-5Si (atomic%). The powder alloys were produced with a high pressure gas atomization (HPGA) process to obtain a high fraction of metal injection molding (MIM) quality powder ({dollar}rm Dsb{lcub}84{rcub} < 32mu m){dollar}. The powders were consolidated either by P/M hot extrusion or by vacuum sintering. The extruded materials were near full density with grain sizes ranging from 30 to 50 {dollar}mu{dollar}m. The vacuum sintering conditions produced samples with density ranging from 87% to 99% of theoretical density, with an average grain size ranging from 26 {dollar}mu{dollar}m to 104 {dollar}mu{dollar}m. Mechanical property testing was conducted on both extruded and sintered material using small punch test. Tensile tests were conducted on extruded bar for comparison with the punch test data. Punch tests were conducted from 25{dollar}spcirc{dollar}C to 550{dollar}spcirc{dollar}C to determine the yield strength, and fracture energy for each alloy as a function of processing condition. The ductile to brittle transition temperature (DBTT) was observed to increase with an increasing silicon content. The Fe-15Al-2.8Si alloy was selected for more extensive testing due to the combination of high temperature strength and low temperature toughness due to the two phase {dollar}alpha{dollar} + DO{dollar}sb3{dollar} structure. The extruded material developed higher yield strength at temperatures below the DBTT, but the sintered material developed higher strengths above the DBTT. The fracture energy of these alloys was higher at all test temperatures, which indicated the importance of grain size and pore interaction with crack propagation. This investigation provided a framework for understanding the effects of silicon in powder processing and mechanical property behavior of Fe-Al-Si alloys.