Chemistry
1. The anti-phase boundary (APB) strengthening is the main strengthening mechanism for Ni superalloys. What is the APB. How does the APB strengthening happen? (15 points)
2. Ni superalloys are the choice for mechanical structures in space applications at 650~1,100°C because they provide both high strength and good oxidation/corrosion resistance. For the majority of engineering materials, such as Fe, Cu, Al and Ti alloys, their yield strength decreases rapidly with increasing temperature, as shown in Figure 1
(a). Nevertheless, the yield strength of Ni superalloys increases with increasing temperature until close to the alloys’ melting point, as shown in Figure 1
(b). Please explain why they behave so uniquely? (25 pts)
