Microstructure and Mechanical Properties of Borided Inconel 625 Superalloy

Ali Gunen,Erdogan Kanca

doi:10.1590/s1517-707620170002.0161

Abstract

The Ni- based superalloy Inconel 625 is extensively used owing to its high strength, excellent fabricability, good weldability and outstanding resistance to high temperature corrosion against aggressive environments. However, despite its unique properties and extensive use, its wear resistance is in some cases unsatisfactory. In this study, Inconel 625 was subjected to boriding treatments at different temperature and different durations. Microstructural characterization was made by conventional methods (scanning electron microscopy, optic microscopy, X-ray diffraction analysis) and mechanical characterization was made by microhardness and micro-abrasion wear test. Micro-abrasion wear tests were conducted against a AISI 52100 steel under 5, 7.5 and 10 N load in a 25 wt.% SiC slurry at room temperature. Microstructural results revealed that multi-phase boride layer (nickel boride, chrome boride and iron boride) and silicide layer were formed. The hardness and thickness of the boride layers were found to be 1175--2432 HV0.1 and, 6.61 -- 92.03 I¼m, respectively. Depending on the boriding temperature and time. In spite of silicide layer formation the wear resistance of borided Inconel 625 alloy increased up to 8 times thanks to the increase in the surface hardness which was caused by boriding process. The boriding treatment caused a transition in the wear mechanism. While grooving was observed in the untreated Inconel 625 samples, mixed (grooving and rolling) and rolling type wear was predominant in the borided samples.

Highlights

Superalloys or high-performance alloys are materials that are capable of retaining their mechanical properties and surface stability even at high temperatures [1]
Microstructural characterization was made by conventional methods and mechanical characterization was made by microhardness and micro-abrasion wear test
In spite of silicide layer formation the wear resistance of borided Inconel 625 alloy increased up to 8 times thanks to the increase in the surface hardness which was caused by boriding process

Summary

INTRODUCTION

Superalloys or high-performance alloys are materials that are capable of retaining their mechanical properties and surface stability even at high temperatures [1]. Superalloys are characterized by their inherent resistance to oxidation and corrosion, resistance to thermal creep deformation and excellent high temperature mechanical strength Because of these properties superalloys are used in many advanced engineering applications such as turbo aircraft and superchargers turbine engines, land-based and aircraft gas turbines, rocket engines, chemical, and petroleum plants and other challenging environments [1-3]. For this reason, many processes were developed in order to improve the tribological properties of Nibased Inconel 625 by applying protective coatings with methods such as plasma spray coating, selective laser melting, CVD aluminide coating, nitridig, etc. The purpose of this study, is to investigate the micro-abrasion wear behavior of Ni-based Inconel 625 superalloys, borided at different temperature and durations, under different loads in a 25 wt.% SiC slurry.. effect of boriding parameters on wear resistance and wear mechanisms of Ni-based superalloy are evaluated

MATERIALS AND METHODS

RESULTS AND DISCUSSIONS

Microhardness and thickness of produced layers

CONCLUSIONS