Microstructure and Properties of Plasma-Nitrided Fe-Based Superalloy Fe-25Ni-15Cr
- PDF / 3,531,354 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 94 Downloads / 152 Views
TION
SUPERALLOYS are commonly used in the aerospace and locomotive industries to fabricate turbine disks, blades, and other critical parts of the aero-engine and locomotive turbocharger[1] owing to their good fatigue, creep properties, and corrosion resistance, where they are subjected to high temperature. Nevertheless, the low hardness and poor wear resistance at high temperature have restricted their applications. Therefore, the surface treatments that can improve surface hardness and antiwear properties while maintaining excellent corrosion resistance have great potential to extend their application field. Plasma nitriding technology has been widely applied to ferrite steels as well as austenite stainless steel. However, a critical disadvantage associated with nitriding XIAOLEI XU, ZHIWEI YU, CAIYUN HOU, WEIXIU SONG, and YINGZHU WANG are with the Department of Materials Science and Engineering, Dalian Maritime University, P.R. China. Contact email: [email protected] Manuscript submitted November 9, 2016. Article published online May 15, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
alloys with high Cr content is that, due to the precipitation of chromium nitrides in the nitrided layer, the improvements in surface hardness and tribological properties are always accompanied by a significant loss in corrosion resistance for the traditional plasma nitriding process[2–4] (process temperatures above 773 K (500 C) or a long duration). To overcome this problem, a low-temperature plasma nitriding technique has been developed.[5] A low-temperature plasma nitriding process of Fe-Cr-Ni austenite stainless steels would produce a thin layer of high hardness with excellent corrosion resistance on the steel surface, which is precipitation free and composed of a single phase termed expanded austenite cN.[5–8] The cN can be described as a supersaturated interstitial solid solution of nitrogen in the expanded and distorted face-centered-cubic (fcc) lattice of c-Fe. However, its crystallographic structure is still a controversial issue. The cN has been variously described as having a tetragonal, or triclinic lattice, an fcc lattice with either a high density of stacking faults or compressive strain, or both.[9,10] Further, the nature of the cN has been investigated recently.[11–13] Compared with austenite stainless steel, a
VOLUME 48A, JULY 2017—3357
few studies have been reported on the nitrided superalloys, but mostly on the Ni-base superalloys,[12,14–16] which also give such a cN phase when subjected to low-temperature plasma nitriding. The nitrided layer on some austenite stainless steels or Ni-base superalloys obtained at low temperature is complex. It is constituted of two or eventually three distinct layers.[7,12,14,17] The X-ray diffraction (XRD) patterns recorded from the expanded austenite layers exhibit two or three sets of distinct expanded austenite reflections (cN1, cN2, or cN3),[12,14,17] shifted to lower diffraction angles compared to the substrate peaks, which are considered generally as austenite containing two d
Data Loading...
