The Effects Of Mo、Ti、Fe On Microstructure And Properties Of Laves Phase Strengthened Cr-10Ta Alloy

Laves-phase TaCr₂ intermetallic compound is expected to work as one of novel candidate high-temperature structural materials for applications on aircraft engine because of its excellent mechanical properties at high temperature. However, its application is hindered by the severe room-temperature brittleness. In the Ta-Cr alloy systems, based on the ductile second phase Cr solution matrix with the reinforcement phase Laves phase TaCr₂, the appropriate alloying element addition can be used for improving the room-temperature brittleness in order to obtain a state-of-the-art superalloy with the excellent comprehended mechanical properties.In the paper, as the object of studying Laves-phase TaCr₂ strengthened Cr-10 Ta alloy, the Cr-10 Ta alloys with the Mo, Ti and Fe additions were prepared by the mechanical alloying and the following hot-pressed sintering technology. The effects of alloying elements on the microstructure and properties of Cr-10 Ta alloys were studied systematically by using the test methods of OM, XRD, SEM and EDS.The results of study show that the average grain sizes of Cr-Ta-Mo powders milled for 25 h are 21.3-93.5nm in the five components of Cr-10 Ta, Cr-10Ta-5Mo,Cr-10Ta-10 Mo, Cr-10Ta-15 Mo and Cr-10Ta-20Mo（at.%）. The room-temperature stable C15 Laves phase TaCr₂ is obtained in the Cr-10 Ta and Cr-10Ta-5Mo alloy,while the 15%Mo and 20%Mo addition can impel the phase transition of Laves phase, where the unstable C14 Laves phase is obtained. Mo can form ternary Laves-phase（Ta, Mo）Cr₂ in the alloys. In the ternary Laves-phase, Mo preferentially occupy the Ta sites. The optimum amount of Mo is 20%, density is 94.6%, approach the full density, Vicker hardness is 6.89 GPa, the fracture toughness is above 7.91MPa√m, the yield strength and compressive strength reach 2635 MPa and 3364 MPa respectively, and the compressive strain is up to 6.7%, the adding of Mo provide significant toughening.The average grain sizes of Cr-Ta-Ti powders milled for 25 h are 33.2⁹0.7nm in four components of Cr-10Ta-10 Ti, Cr-10Ta-20 Ti, Cr-10Ta-30 Ti and Cr-10Ta-35 Ti.The room-temperature stable C15 Laves phase TaCr₂ is obtained in the four alloys,Ti addition can not impel the phase transition of Laves phase. Ti can form ternary Laves-phase（Ta, Ti）Cr₂ in the alloys. In the ternary Laves-phase, Ti preferentially occupy the Ta sites. With the increase of Ti content from 10% to 35%, the hardnessincreases, the biggest Vicker hardness is 10.3GPa when Ti content is 35% and the density of all alloys is above 94.2%. But, the fracture toughness and compressive strength show a large drop with the increase of Ti content, compressive strain can not show at room temperature. The fracture morphology of Cr-10 Ta alloy is the intergranular ductile fracture, appearing a small amount of dimples in the local area, but the fracture morphology of Cr-10Ta-35 Ti with a large amount of cleavage platform and the small cavitys of diameter 2μm is the transgranular brittle fracture,the adding of Ti significantly reduce the plasticity of Cr-10 Ta alloy.The average grain sizes of Cr-Ta-Fe powders milled for 25 h are 22.2-72.2nm in four components of Cr-10Ta-10 Fe, Cr-10Ta-20 Fe, Cr-10Ta-30 Fe and Cr-10Ta-35 Fe.The room-temperature stable C15 Laves phase TaCr₂ is obtained in the Cr-10 Ta,Cr-10Ta-10 Fe and Cr-10Ta-20 Fe alloy, while the 35%Fe addition can impel the phase transition of Laves phase, where the unstable C14 Laves phase is obtained.The optimum amount of Fe is 20%, density is 98.3%, Vicker hardness is 7.14 GPa,the fracture toughness is above 7.91 MPa√m, the yield strength and compressive strength reach 2120 MPa and 2461 MPa respectively, and the compressive strain is up to 4.9%, the adding of Fe provide significant toughening, but the adding of Mo is more effective than Fe.