Microstructure and wear resistance performance of Cu–Ni–Mn alloy based hardfacing coatings reinforced by WC particles

Highlights

• A WC/Cu–Ni–Mn composite is developed by an oxy-acetylene weld hardfacing method.

• WC particles did not dissolve during the weld hardfacing process.

• No defects are observed in the composite or at the interface of WC/Cu–Ni–Mn alloy.

• The composite is 4 times more resistant against wear than high-Cr cast iron.

• Wear mechanisms are the plastic extrusion of the matrix and the fracturing of WC particles.

Abstract

A Cu–Ni–Mn alloy based hardfacing coating reinforced by WC particles is deposited on steel substrates by a manual oxy-acetylene weld hardfacing method. Microstructure and wear resistance performance of the fabricated hardfacing coatings are investigated. There are no cracks or other defects observed in the hardfacing coating. Uniform distributed WC particles in the composite hardfacing coating are not dissolved, and its volume fraction is up to about 63%. A sound bond is formed at the interface of WC and Cu–Ni–Mn alloy, and the bond between the coating and the steel substrate is reliable. With silica sands, the wear resistance performance of the composite hardfacing coatings is about 4 times better than that of the high-Cr cast iron, and its volume loss presents approximately a linear relationship with the sliding distance. The main wear mechanisms are the plastic extrusion of the Cu–Ni–Mn matrix and the fracturing of WC-reinforcement particles under three-body abrasive wear condition in this paper.

Introduction

As for engineering machines and components, there is an ever-increasing demand for wear resistant materials, which can reduce wear and thus extend their service life. Hardfacing process is an effective way to improve wear resistance performance by applying a wear resistant coating on the surface of softer and tougher inner materials [1], [2], [3]. Such composite hardfacing coatings, commonly known as particle-reinforced metal-matrix composites (PRMMCs), can significantly improve the tribological properties of components by employing a metallic alloy as the matrix and the ceramic particles as reinforcements. In addition, compared with fiber reinforced metal-matrix composites (MMCs), PRMMCs can also be fabricated with low cost and obtain nearly isotropic properties. Hence, it has been widely studied and applied [2], [4], [5], [6], [7].

The wear resistance performance of PRMMCs depends greatly on the mechanical properties of the metal matrix alloy. As a matrix alloy, Cu–Ni–Mn ternary alloy is formed by adding Mn into the base binary Cu–Ni alloy. The addition of Ni and Mn elements greatly improves the degree of solid solution strengthening, and thus can improve significantly its strength and elasticity. Many researchers have investigated the excellent properties of Cu–Ni–Mn alloys [8], [9], [10], [11], [12], [13], such as the intense age hardening characteristic, high intensity, low melting points, mechanical and corrosion resistance properties. Qihan Pan has made a critical and comprehensive review on the nominal composition of Cu₆Ni₂Mn₂ alloy [12]. This alloy has the excellent properties after the aging treatment: 1) high tensile strength, σ_b ≥ 1470 MPa, reaches the strength value of high strength steels; 2) high microhardness, about 450 HV; 3) high elastic modulus, E = 143 GPa; 4) good ductility (elongation δ ≥ 2%); and 5) low melting point of only 1050 °C. Therefore, such Cu–Ni–Mn alloy with these good mechanical characteristics can be a potential matrix material for MMCs.

To fabricate PRMMCs, carbide and oxide particles are often selected as reinforcement particles, which are homogenously dispersed in the metal matrix alloy. During the process of adding the reinforced particles into the metal matrix, if the reinforced particle does not show the good compatibility with the metal matrix, it often leads to cracks and some other defects at the interface of the metal matrix and the reinforcements, and even results in the segregation of particles and the metal matrix.

Tungsten carbide (WC) is widely selected as the reinforcement particles in wear resistance applications [14], [15], [16], [17], [18], [19]. WC is a kind of transition metal carbides, which has a low coefficient of thermal expansion, a certain amount of plasticity and can retain its room temperature hardness up to 1400 °C without any phase change. Furthermore, WC has limited solubility in copper and does not form complex interfacial intermetallic layers with copper alloys [19]. The wear resistance of WC/Cu–Mn–Ni brazing coating has been investigated under the dry sliding condition [20]. The introduction of WC particles has a positive effect on the final wear resistance performance, which is related to the size and content of WC particles in the composite coating. Previous publications also prove that WC has the good wettability with the Cu₆₀Ni₂₀Mn₂₀ alloy [21], [22].

In this paper, a Cu–Ni–Mn hardfacing coating reinforced with WC particles is deposited on steel substrates by a manual oxy-acetylene weld hardfacing method. Its microstructure and wear behaviors under three-body abrasive wear condition are investigated. The wear resistance performance of the fabricated hardfacing coatings is compared with a conventional high-Cr cast iron, and the wear mechanisms are analyzed.