Effect Of Alloying On Thermal Sability Of In-situ Synthesis Of Cr-77.5Nb Tow-phase NbCr₂/Nb Alloy

NbCr2/Nb (Cr-77.5Nb) alloys was prepared by mechanical alloying and reactivehot pressing in this paper. On the basic of that, the effect of B4C、Nd2O3and Moadditions on the thermal stability of NbCr2/Nb (Cr-77.5Nb) alloys was investigatedafter thermal exposure at1200℃in vacuum for a long time.The main results were asfollows:After thermal exposure at1200℃for a long time, the relative density of(Cr-77.5Nb)-0.25at.%B4C、(Cr-77.5Nb)-0.5at.%B4C alloys kept better, while, themicrostructure of alloys had no obvious coarsening and pore. After100h thermalexposure, compared (Cr-77.5Nb)-0.25at.%B4C alloy with the original alloy, Vickershardness and the yield strength decreased from6.10GPa and1867MPa to5.45GPaand1627MPa, while, compressive strength and strain varied from2973MPa and14.7%to3043MPa and22.8%, respectively. Compared (Cr-77.5Nb)-0.5at.%B4Calloy with the original alloy, after50h thermal exposure, compressive strength and theyield strength declined from3048MPa and1998MPa to2788MPa and1583MPa,respectively. While, Vickers hardness was declined from6.02GPa to5.32GPa, andstrain reachd from12.7%to20.7%at100h. Before and after thermal exposure, thesamples of alloys with two compositions had no cracks, and fracture toughnessmaintained well. The results indicated that the Cr-77.5Nb with B4C addition couldkeep a good thermal stability in a way, because the fracture toughness maintainedwell, but Vickers hardness and the yield strength at room temperature were not good.During the entire vacuum thermal exposure process at1200℃for a long time,the relative density of (Cr-77.5Nb)-0.125at.%Nd2O3alloy kept up to98%, themicrostructure of alloy had no obvious coarsening. After100h thermal exposure,compared (Cr-77.5Nb)-0.125at.%Nd2O3alloy with the original alloy, Vickershardness, compressive strength and the yield strength of alloy reduced from6.42GPa、3193MPa and2227MPa to5.68GPa、3051MPa and1822MPa, respectively. Then, thestrain reached from13%to18.8%. Before and after thermal exposure, to the alloy,fracture toughness maintained well, and strain increased gradually. The resultsshowed that the Cr-77.5Nb with Nd2O3addition could maintain a good thermalstability, which resulted from the fracture toughness and the mechanical properties at room temperature kept well.During the whole exposure process at1200℃for a long time, the relativedensitys of (Cr-77.5Nb)-2.5at.%Mo、(Cr-77.5Nb)-5at.%Mo、(Cr-77.5Nb)-7.5at.%Moand (Cr-77.5Nb)-10at.%Mo alloys kept up to98%，while, the microstructure of alloyswere small, uniform distribution, and had no obvious coarsening. Among the alloys,the thermal stability of the (Cr-77.5Nb)-2.5at.%Mo alloy was kept better, during theentire exposure process, strain and fracture toughness of alloy maintained well. After100h thermal exposure, Vickers hardness, compressive strength and the yield strengthof alloy reached to6.19GPa、3040GPa and2004GPa, respectively.In a word, the thermal stability of NbCr2/Nb (Cr-77.5Nb) alloys with Moaddition was maintained better than those of alloys with B4C and Nd2O3additions.