Simultaneously improving mechanical properties and oxidation resistance of Ti-bearing high-entropy superalloys at intermediate temperature via silicon addition

Ti-bearing high-entropy superalloys(HESAs)often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures.Here we showcase that minor Si addition can effectively mitigate the intergranular embrittlement and improve the oxidation resistance of the a(Ni_(2)Co_(2)FeCr)_(92) Ti_(4)Al_(4) HESA at 700℃ simultaneously.Experimental analysis revealed that the intergranu-lar G phase induced by 2 at%Si addition can effectively suppress the inward diffusion of oxygen along grain boundaries at 700℃,thus enhancing the tensile ductility of the alloy from∼8.3%to∼13.4%.Be-sides,the 2 at%Si addition facilitated the formation of a continuous Al_(2)O_(3) layer during oxidation,con-tributing to a remarkable reduction in the growth rate of the oxide scale to a quarter of the Si-free HESA.Our results demonstrate that Si can be a favorable alloying element to design advanced HESAs with syn-ergistically improved thermal-mechanical performance.

Surface modification of plasma nitriding on AlxCoCrFeNi high-entropy alloys

Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided Al content(i.e.,x values in molar ratio,x=0.1-0.8)to develop wear-resistant structural materials.Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase,forming nanoscaled nitrides(AIN and CrN)precipitations near the surface.Nitriding promotes the hardness of present alloys with values widely ranging from 276 HV to 722 HV.Interestingly,the higher content the Al,the smaller thickness the nitrides layer,but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase.Significantly,plasma nitriding considerably improves the wear re sistance of AlxCoCrFeNi HEAs by 4-18 times.