Feb_March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 8 2 6 TECHNICAL SPOTLIGHT IMPROVING COMPONENT LIFE CYCLES THROUGH MATERIALS ENGINEERING Advanced materials engineering is being used to solve component life cycle improvement challenges in extremely harsh working conditions. T he term life cycle refers to the work- ing life span of a product, for exam- pleanindependentcomponentlike a cutting tool or railroad frog, or a piece of machinery such as a turbine blade, boiler tube, or precision gear. A component’s life cycle is the time in service before it fails to function effectively. Variables affecting the predictable life cycle in progressive degradation processes including wear, fatigue, creep, and fracture toughness are listed in Fig. 1. This article discusses examples from various industries where new materials and surface modifications are used to extend the useful life of engi- neering components and equipment. LIFE CYCLE ASSESSMENT Life cycles in all progressive degra- dation processes follow a similar pat- tern: An initial run-in period (Stage I) leads to steady-state operation (Stage II), followed by failure (Stage III). Dura- tion of the steady-state condition is the useful life span of the material. Figure 2 shows how increasing severity of the working environment (from A to B to C) causes a higher rate of degradation and shorter steady-state span, until Stage I converges with Stage III, leading to ear- ly failure. IMPROVING LIFE CYCLE Material life cycle improvement (LCI) can be achieved through surface engineering and modification process- es. Modification of one or more surface properties (e.g., energy, microstructure, roughness, chemical composition, and hardness) can minimize material and energy losses in tribological interaction processes such as wear and friction. Figure 3 shows an example of modifying the surface properties of a gear to improve working life span. Ad- vanced surface engineering processes include chemical and physical vapor deposition (CVD and PVD), diffusion of interstitial and substitutional elements, welding, and thermal spray using heat sources such as laser, plasma, micro- wave, arc, spark, induction, ion, elec- tron, advanced combustion, friction, and solar beam. Fig. 1 — Variables affecting predictable and assessable life cycles of components in progressive degradation processes, including wear, fatigue, creep, and fracture toughness. Fig. 2 — Changing pattern in life cycles based on severity of the environment. In extreme environments (C), Stage I converges into Stage III without going through a period of steady-state operation (Stage II).