HIP technology

Hot isostatic pressing can improve mechanical properties. Whether it is laser SLM forming or electron beam EBM forming, there is a tendency for the strength of the material to decrease and the plasticity to increase after hot isostatic pressing, especially for materials with SLM technology. The reason for this phenomenon is that the cooling rate of the SLM forming process is faster and more martensite is formed in the formed part, which decomposes after HIP annealing, causing the strength of the material to drop and the plasticity to rise. At the same time, the hardness of the material will also change with HIP, with a 5-10% drop in hardness after HIP. Overall, hot isostatic pressing improves the material’s toughness and resistance to fatigue crack extension.

Limitations of hot isostatic pressing treatment

Hot isostatic pressing does not work well on any material and for any defect elimination, and improper setup of the hot isostatic pressing process can have very serious consequences, so the following should be noted when using hot isostatic pressing.

(1) For open defects (defects that extend from the inside of the part to the surface of the part and the external gas medium) hot isostatic pressing does not have any effect on the elimination of defects.

(2) When a large defect (over 2mm) exists within the part it will form a crater on the surface of the part, as shown in Figure 5, and will require welding to repair. When the crater is in a position where a weld repair is not possible, it may result in the scrapping of the part, such as some thin-walled parts, thin-walled parts or blades.

(3) No effect on the elimination of cracks and inclusions defects.

(4) Hot isostatic pressing may cause oxidation of the surface of the part, forming a thin oxide film, preferably between finishing operations.

(5) Hot isostatic pressing may cause severe distortion of the part and measures to prevent distortion should always be considered before doing so.

(6) Improperly set process temperatures and pressures may result in thinning of the wall thickness of the part and, in severe cases, in severe coarsening of the grain size of the part, resulting in poor material properties and scrap of the part.

(7) For alloys with large differences in melting points of alloying elements may result in burnout of low melting point chemical elements.

(8) Not suitable for eutectic alloys, easy to form liquefaction cracks.