Properties Of Titanium Surface Alloyed 316L Stainless Steel

Austenitic stainless steel 316L is widely utilized in petroleum industry, aerospace, chemical processing industries, electric power, nuclear engineering and other fields due to its excellent corrosion resistance, comprehensive mechanical properties and processing properties. However, its low hardness and poor wear resistance, as well as a tendency to corroding under the halide ion environment, limit its applications. To solve these problems, this paper proposed to fabricate a titanium surface alloyed layer on 316L stainless steel substrate by means of the double glow plasma surface alloying technique. The component and structure, tribological properties and corrosion properties of the titanium surface alloyed layer have been studied. The main results have been obtained as follows:(1) A gradient distribution of elements in the surface alloyed layer, which means an excellent metallurgical binding between the surface modified layer and 316L stainless steel substrate. The surface roughness of the modified layer increases to 1.34μm, because of the ion bombardment and the deposition of Ti atoms or groups on the substrate surface during the process of plasma surface alloying.(2) After the treatment of plasma surface titanium alloying, Ti-C compound and the intermetallic compounds (Fe2Ti,Cr2Ti and NiTi) were formed in the alloyed layer. Owing to the formation of hard phase, the surface hardness of the alloyed layer is 1305HK0.05, which is much larger than that of the 316L stainless steel substrate with the value of 382 HK0.05.(3) The tribiological properties and mechanism of the titanium surface alloyed layer have been studied by ball-on-disk test. Although the titanium surface alloyed layer doesn't show a friction-reducing effect, it improves the wear resistance of 316L stainless steel obviously and its wear rate is only one-fifteenth of that for untreated 316L stainless steel. Dominant wear mechanisms of 316L stainless steel are ploughing and adhesion, while the wear mechanisms of titanium surface alloyed layer shows lightly abrasion because of the increase of the surface hardness.(4) The electrochemical corrosion properties and mechanism of 316L stainless steel and the titanium surface alloyed layer have been characterized and compared in 0.5 mol/L HCl, 0.5 mol/L NaCl and 0.5 mol/L H2SO4. Results show that the corrosion rate of titanium surface alloyed layer is all lower than that of 316L stainless steel in the three kinds of solution, and the titanium surface alloyed layer presents better corrosion resistance. In the experiment of intergranular corrosion resistance, the 316L stainless steel substrate shows seven kinds of pit structure-Ⅱintergranular corrosion, while almost no intergranular corrosion takes place on the titanium surface alloyed layer.