Current Functional Materials for Wear-Resistant Casting: from Multicomponent Cast Irons to Hybrid High-Boron Alloys

Abstract

The results obtained in the last two decades in the development of functional tribological alloys for the castings working under severe abrasion, erosion, and erosion–corrosion conditions are reviewed. The chemical composition, microstructural features, mechanical and tribological properties of (a) multicomponent cast irons, (b) Fe–C–B alloys with an increased (1–3.5 wt.%) boron content, and (c) hybrid abrasive-resistant alloys designed by combining different alloying principles are analysed. The necessity for the formation of a heterophase structure consisting of multitype hard compounds (carbides, borides, and carboborides) distributed in a secondary-hardened martensite matrix is highlighted as a key approach to reaching an advanced abrasive wear resistance of the cast components. The target structural state can be obtained by simultaneous adding several strong carbide-forming elements (Ti, W, Mo, V, and Cr) taken in the same amount (by analogy with high-entropy alloys). This allows the elements to compete with each other to form different phases during crystallization, which ensures the general refinement of the alloy structural constituents. The advantages of partial replacement of carbon with boron in Fe-based alloys are emphasised that allows the formation of boride and carboboride compounds having much higher hardness compared to carbides. This makes it possible to achieve an advanced level of wear resistance in the absence (or at low content) of alloying elements, benefiting from a significant reduction in the cost of the alloy. The influence of alloying elements on the physical and mechanical properties of boride phases is analysed; prospects are outlined, and novel (‘hybrid’) alloys combining the multialloying principle with high boron content are presented. The main technological approaches applied to improve the mechanical and tribological properties of boron-containing wear-resistant casting are described.

Keywords

• multicomponent cast iron
• high-boron cast iron
• wear resistance
• microstructure
• boron
• carbides
• borides