Hot isostatic pressing (HIP) is used to eliminate closed pores remaining inside powder-metallurgy parts and castings. Which describes the method correctly?

Answer: C. At high temperature, an inert gas such as argon is used as the pressure medium to apply an equally high pressure from all directions

In HIP the part is placed in a pressure vessel and, while heated to high temperature, an equal pressure of about 100 MPa or more is applied from all directions by an inert gas such as argon. Closed internal pores collapse and disappear by creep and diffusion, raising density and fatigue strength without greatly changing the shape. It is also used to eliminate pores in turbine-blade castings and in metal parts made by additive manufacturing. Open pores connected to the surface do not collapse because gas enters them, so the part is first sintered until the pores close, or the powder is sealed in a metal container (capsule) for treatment. Using a rubber mold at room temperature is cold isostatic pressing (CIP), and pressing in one direction while passing current is a method such as spark plasma sintering.