Cold sprayed WC reinforced maraging steel 300 composites: Microstructure characterization and mechanical properties

Highlights

• WC reinforced maraging steel 300 composites were fabricated by cold spray.

• Distribution of WC particle in composite were studied by X-ray Computed Tomography.

• High WC retainability was achieved by high pressure cold spray system.

• Solution-aging treatment can significantly improve the tensile and wear performance.

• Cohesive bonding of WC particle was improved by heat treatment.

Abstract

Maraging steel 300 (MS300) is a precipitation-strengthening iron–nickel alloy with outstanding properties such as good mechanical strength, weldability and corrosion resistance. However, the poor wear resistance has limited the application. In this work, high-performance WC reinforced MS300 composites were fabricated by high-pressure cold spray, which enables the additive manufacturing of bulk material well below its melting point. XRD analysis shows that no phase transformation occurred either to the WC reinforcements or the MS300 matrix. The distribution and morphology of the WC particles in the composite samples were characterized by X-ray computed tomography (XCT). The results show that a high retainability (85.4%) of WC particles was obtained at high working parameters (N₂, 5 MPa, 900 °C), and the solution-aging treatment resulted in decreased WC volume fraction and smoothing of WC shape. Microstructure observation of WC evolution shows that a thick diffusion layer was formed around the WC particle after solution-aging treatment significantly improving the interfacial bonding. Due to the more severe plastic deformation and higher WC retainability, the as-fabricated samples with higher propelling gas pressure demonstrate a higher tensile strength and better wear resistance. It is found that a higher solution temperature (1000 °C) can lead to an enhanced cohesive bonding within the composite. Finally, the solution-aged composite shows an excellent wear resistance under the improved WC bonding and precipitation hardening.

Introduction

Maraging steel 300 (MS300) is an iron–nickel alloy with absence of carbon, which uses elements such as molybdenum, cobalt, titanium and aluminum as substitutes to produce precipitation-hardening in iron-nickel martensite [1,2]. Based on the precipitation of intermetallic compounds, the maraging steel 300 presents outstanding properties such as good mechanical strength, toughness, weldability and resistance to crack propagation. It has been widely applied in the fields like automotive, aircraft and aerospace, and tool and die industries, such as rocket motor casings and landing gears, conformal cooling channels, shafts, and fasteners. Upon the treatment procedures of solution and aging, outstanding mechanical properties and stable microstructure can be achieved on MS300 through the formation of lath martensite with high dislocation, solution strengthening of alloy elements and precipitation strengthening by intermetallic compounds [3,4]. Nevertheless, with the development of industry technology, it brings forward an increasing demand of comprehensive performance for maraging steel 300, especially the high tribological performances of MS300, which can extend its applications [5].

WC-reinforced metal matrix composites (MMCs), combined metallic properties with ceramic, have been fabricated by different manufacturing methods and widely investigated in recent years [[6], [7], [8]]. For example, the powder-bed based AM technologies via laser or electron beam have been proposed for the fabrication of WC-based MMCs [[9], [10], [11]]. It is also reported that the WC-reinforced MMCs are fabricated by using conventionally high temperature processes such as high velocity oxy-fuel (HVOF) [12,13] and laser cladding [14,15], where the high cohesive strength is achieved by partial or complete melting of feedstock particles. However, the serious oxidation, phase change and even decarburization of carbide phase cannot be avoided in these high-temperature fabrication methods, which may result in the deterioration of mechanical properties.

To eliminate the degradation of MMCs properties under high processing temperature, the newly emerging cold spray (CS) (or known as cold gas dynamics spray, kinetic spray) [16,17] has attracted increasing attentions as a solid-state deposition technology. Prior to the impact onto substrate, the micro-sized feedstock particles are accelerated to high velocity (300–1200 m/s) by a supersonic gas flow (air, nitrogen or helium) through a de-Laval nozzle [18]. Owing to the low temperature of the propelling gas below its melting point (about 300–1000 °C) and short interaction time, the deposited particles can well maintain the solid state [[19], [20], [21]]. The high-velocity impact of metallic particle onto substrate can result in serious plastic deformation within several tens of nanoseconds. Similar with explosive welding, the breaking and extrusion of original oxide-film on feedstock particle can promote the high-quality metallurgical bonding within CS sample [20,22]. As a result, the CS technology enables the retainability of its original chemical composition and properties in feedstock, and effectively minimize the serious oxidation, phase change and thermal stresses in high-temperature processing [23,24]. For the moment, the CS technology has been successfully applied in the fabrication of temperature-sensitive materials like aluminum [25,26] and copper [17], high performance alloys like Ti6Al4V [27,28] and Inconel [29,30] as well as various MMCs with different reinforcements [8]. By accounting the high production rate and no limitation of fabrication size, CS has been recognized as an effective method for additive manufacturing [31,32] and dimensional damage repair [25,33].

In the same manner, the unique “cold” feature of CS technology can effective protect the WC particles in MMCs material from oxidation and decarburization. Recently, the WC reinforced MMCs have been frequently reported fabricated by CS. Lioma et al. [34] fabricated WC-Ni coatings by using a low-pressure CS system with mechanical mixed powders and sintered agglomerated powders. However, only 11–29% of WC particles were retained in the as-sprayed coatings. Similarly, Melendez et al. studied [35] the microstructure evolution and coating properties of WC reinforced MMCs with Ni as binder phase. Alidokht et al. [36] reported that the wear resistance of Ni coating fabricated by high pressure CS system can be significantly improved through the reinforcement of 36.2 vol% WC particles, but with a low WC retainability of 29.0%. Besides, efforts were also made to fabricate the WC-Co coating [37,38] by CS within the past decades. The extremely high deposition parameters were used to promote metallic bonding by inducing sufficient plastic deformation of feedstocks. It can be concluded that the above-mentioned works have a typical low retainability of WC in as-sprayed coating compared with the feedstock. Furthermore, the low processing parameters cannot obtain sufficient mechanical property and microhardness to realize their industrial application.

Therefore, this work aims to use high-pressure CS system to manufacture high-performance WC reinforced maraging steel 300 (MS300) composites. To the author's knowledge, few studies [11] have been made on the fabrication of high-performance MS300 by CS. The solution-aging treatments were conducted to promote the inter-particle diffusion, stress releasing and precipitation strengthening and hardening. A systematic study was carried out focusing on the microstructure characterization and mechanical properties. The X-ray computed tomography was applied to investigate the distribution and morphology of WC particles within the CS WC/MS300 composites. The EBSD and SEM observation were used to study the microstructural evolution. At last, the tribological and tensile properties of CS WC/MS300 composites were studied.