Research On The Microstructure And Properties Of Plasma Carbonitriding Of Hastelloy C-276 Nickel-based Alloy

Pipes,pumps,valves and other devices made from nickel-based corrosion resistant alloys can wear and even fail under high mechanical loads,limiting their use in wear-resistant service.In this paper,Hastelloy C-276,a nickelbased corrosion-resistant alloy,was used as the base material for the preparation of modified layers at different temperatures(395 ℃,425 ℃,455 ℃,485 ℃)and times(6 h,9 h,12 h,15 h)using plasma carbonitriding technology.The main results of the study are as follows:In this paper,Hastelloy C-276,a nickel-based corrosion-resistant alloy,was used as the base material to prepare the modified layer at different temperatures(395 ℃,425 ℃,455 ℃ and 485 ℃)and times(6 h,9 h,12 h and 15 h)using plasma carbonitriding technology.The main results of the study are as follows:(1)After plasma carbonitriding of nickel-based alloy C-276,N and C atoms entered the austenitic lattice,forming an expanded austenitic S phase contain ing nitrogen and carbon,and the CrN phase precipitated from the seepage layer with the increase of the carbonitriding temperature and time.The layer thickness increased linearly with increasing treatment temperature and was proportional to the square root of the treatment time.The activation energy of nickel-based alloy C-276 was calculated to be 0.41 eV,which indicates that the layer growth kinetics are controlled by the diffusion of nitrogen and carbon.(2)The surface hardness of the matrix specimens after plasma carbonitriding treatment was increased to a different extent.Under the condition of 12 h treatment time,the surface hardness of the carbonitriding specimens increased significantly with the increase in temperature,which was about 3-4times that of the matrix.Under the condition of 420 ℃ treatment temperature,the hardness of 6 h treatment specimens and 9 h treatment specimens was only2-3 times that of the matrix,while the hardness of 12 h treatment specimens and15 h treatment specimens was about four times that of the matrix after a longer period of carbonitriding treatment,which was a more obvious increase.(3)The frictional wear performance of the specimens under the two different parameters of the process shows that at a lower processing temperature(≤395 ℃)and a shorter processing time(≤9 h)due to the short processing time of carbonitriding,not enough to generate a sufficient thickness of S-phase layer,a more serious adhesive wear occurred;at a higher temperature and a longer time of carbonitriding treatment to generate a thicker S-phase layer and hard phase CrN to give the matrix excellent wear resistance,so that the surface wear of the specimens is greatly reduced,although there is wear but did not cause serious damage,the wear mechanism is abrasive wear and oxidation wear.(4)Temperature has a significant effect on the corrosion resistance of the C-276 coextrusion layer.Treatment at a higher temperature of 485 ℃ causes the matrix to be Cr-poor,which reduces its corrosion resistance,and at lower temperatures(<450 ℃)the carbonitride-treated samples show better corrosion resistance than the matrix samples.