Properties of Spark Plasma Sintered Compacts and Magnetron Sputtered Coatings Made from Cr, Mo, Re and Zr Alloyed Tungsten Diboride

Tomasz Mościcki,Maria Wiśniewska,Dariusz Garbiec,Rafał Psiuk,Joanna Radziejewska

doi:10.3390/coatings11111378

Abstract

To enhance the properties of tungsten diboride, we have synthesized and characterized solid solutions of this material with chromium, molybdenum, rhenium and zirconium. The obtained materials were subsequently deposited as coatings. Various concentrations of these transition metal elements, ranging from 0.0 to 24.0 at.%, on a metals basis, were made. Spark plasma sintering was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of both samples (sintered compacts and coatings) were examined using energy dispersive X-ray spectroscopy and X-ray diffraction. Microindentation was utilized to measure the Vickers hardness. X-ray diffraction results indicate that the solubility limit is below 8 at.% for Mo, Re and Zr and below 16 at.% for Cr. Above this limit both diborides (W,TM)B2 are created. Addition of transition metals caused decrease of density and increase of hardness and electrical conductivity of sintered compacts. Deposited coatings W1−xTMxBy (TM = Cr, Mo, Re, Zr; x = 0.2; y = 1.7–2) are homogenous, smooth and hard. The maximal hardness was measured for W-Cr-B films and under the load of 10 g was 50.4 ± 4.7 GPa. Deposited films possess relatively high fracture toughness and for WB2 coatings alloyed with zirconium it is K1c = 2.11 MPa m1/2.

Highlights

Nowadays the rise of a broad class of compounds comprising heavy transition metal (TM) and light-element atoms, like nitrides, carbides, and borides can be seen
The minimum holding time required to obtained near full dense sintered compacts is 8 min and a couple of seconds before this time the plateau of the sintering curves is clearly seen. This means that sintering is completed under certain conditions
A further increase in the holding time resulted in further upper punch movement. This is related to the reactive sintering and creation of diborides from pure elements resulted in an increase in the density of the sintered body and finished between 14 and 15 min without any further densification

Summary

Introduction

Nowadays the rise of a broad class of compounds comprising heavy transition metal (TM) and light-element atoms, like nitrides, carbides, and borides can be seen. Such compounds possess excellent mechanical properties such as high hardness and high wear resistance, refractory properties and good thermal and electrical conductivity resulting from the concurrently high valence electron density and strong covalent bonding in these compounds [1,2]. A major challenge remains in that the applications are to produce reliable tool components made of these materials in a relatively simple and time-consuming manner This challenge is partly resolved by deposition of thin films [5,6,7,8] developing machinable materials [3] or new methods of sintering [9]. The theoretical studies have showed that WB2 doped by TM can possess the very high hardness above 40 GPa [1,5]

Objectives

Methods

Results

Conclusion