Mechanical Strengthening and Microstructural Evolutions of Ni-B Based Hardfacing Alloys Influenced by Titanium Additions

Zeblon Meshack Ebimobowei

doi:10.11648/j.am.20190802.11

Abstract

The microstructure and mechanical behaviour of Ni-B binary alloys have been enhanced in this study by varied titanium additions. The alloys investigated were chosen from the nickel-rich region of the Ni-B-Ti system. The microstructure of the alloys was examined using Optical Microscope (OM) and Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-ray Analyzer (EDXA). The addition of titanium led to the formation of various complex phases and a ternary phase τ was observed in the study. The addition of titanium to the Ni-B alloys was found to enhance the mechanical properties of the ternary alloys. Microhardness value of the alloys was observed to increase from 216.2 HV with zero Ti in Ni-B alloys to 1530.7 HV in alloys with 11 wt. % Ti. The stiffness of the alloys was also found to increase as deduced from elastic modulus value of 513.77 to 1046.51 N/m2 in Alloys C. Remarkable improvement in physical properties of the Ni-based ternary alloys is due to the formation of various hard boride phases and grain size reduction occasioned by the increase in titanium content.

Highlights

Due to the inability of materials to meet the need of engineers, surface treatments of materials become pertinent for their optimum performance
For Alloy A with 2 wt. % Ti addition and quenched from the liquidus, the primary phase observed in both Scanning Electron Microscope (SEM) and optical microscope images is the block-like Ni(α) phase shown in Figures 3a and 3b
The elemental compositions of the identified phases in the microstructures were analyzed with Energy Dispersive X-ray Analyzer (EDXA) and the results shown in spectra images, Figures 4a, 4b and 4c for Ni (α), Ni-Ni3B and Ni3B respectively

Summary

Introduction

Due to the inability of materials to meet the need of engineers, surface treatments of materials become pertinent for their optimum performance. Recently the problem of wear, abrasion, hot corrosion as well as poor hardness and poor stiffness of materials have been addressed by surface treatments and hardfacing techniques [1,2,3,4,5,6]. Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. It generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene. Hardfacing technique involves the preparation and application of hard alloy coatings on surface of materials. These alloys usually contain several hard phases (borides, carbides and silicides) made up of titanium, chromium, vanadium etc. These alloys usually contain several hard phases (borides, carbides and silicides) made up of titanium, chromium, vanadium etc. and non-metals like boron, carbon and silicon

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