Microstructure And Mechanical Properties Of Rapid Solidified Al-Fe-Cr-Ti Elevated Temperature Alloy

Nanoquasicrystalline particle reinforced Al-Fe-Cr-Ti elevated temperature alloydraw great interest in aerospace and aviation industry due to its outstanding properties,such as, low density, high strength and high temperature resistence up to350℃.Recently, researchers all over the world paid lots of attention to its production processesand microstructural characterations. However, the thermal stability and strengtheningmechanism of Al₉₃Fe₃Cr₂Ti₂alloy remain unclear. This work is aim to obtainAl₉₃Fe₃Cr₂Ti₂bulk alloys by using rapid solidification （RS） and powder metallury （PM）technique, investigate the phase transformation of icosahedral quasicrystalline phases（i-phases） after heat treatment by using SEM, XRD and TEM techniques, study thefluence of size and distribution of dispersed second phases on mechanical properties, atlast optimize densification parameters.As the cooling rates decreased, i-phases were formed through Al₉₃Fe₃Cr₂Ti₂moltendroplets at first, followed by Al₃Ti phases, then Al₁₃Fe₄and Al₁₃Cr₂intermetallics, andi-phase disappeared at last. Gas atomization changed from nonequilibrium process toequilibrium process. Nanoquasicrystalline second phases and amorphous matrix wereobserved in as-atomized powders.In the present work, the angles between rotational symmetry axis of i-phase, i.e.,<i2, i5>,<i2, i3>,<i3, i5>, were determined to31.2°,23.4°,39.4°, repectively, by usingthe series tilting technique. In rapid solidified Al-Fe-Cr-Ti system, icosahedral twinswere observed for the first time. After heat treated at450℃, i-phases started to grow up,Al₁₃Fe₄and Al₁₃Cr₂phases with stacking faults and twins were precipitated in the grainboundary. I-phases transformed after heated at500℃: i-phaseâ†'-Al+Al₃Ti, which twophases share coherent orientation relationship as:-Al [-112]∥L12-Al₃Ti [-111],-Al[10-1]∥D0₂₂-Al₃Ti [10-1].Fine graind Al₉₃Fe₃Cr₂Ti₂alloys were prepared by gas atomization, canned vaccumdegassing, cold/hot isostatic pressing, and extrusion/multi-step rolling. Themicrostructure was characterized with fine aluminum grain and second phases fromnano-scale to micro-scale. As-extruded bulk alloy inherited parts of rapid solidifiedmicrostructural features, banded structure with i-phase and intermetallics as precipitates.After multi-step rolling, the microstructure was uniform with intermetallics as secondphases.Al₉₃Fe₃Cr₂Ti₂alloy have excellent comprehensive mechanical properties at roomand elevated temperatures. Ultimate tensile strength （UTS）, yield strength （YS） andenlongation of the as-extruded HE-2sample at20℃and300℃, were578MPa,533 MPa,4.8%and385MPa,356MPa,4%, respectively. The UTS, YS and enlongationof the as-rolled MR-2sample at20℃and300℃, were675MPa,577MPa,4.8%and348MPa,288MPa,11.5%, respectively. When tensile temperature increased,enlongations increased at first, then decreased, and increased at last, intermediatetemperature embrittlement was found around200℃in Al₉₃Fe₃Cr₂Ti₂alloy.