HIP and Heat Treatment of AM Parts- Microstructure and Mechanical Properties and the Effect of Combined HIP and Heat Treatment Cycles Compared to Conventional Processing
Dr Susan Davies (Bodycote Hot Isostatic Pressing AB, United Kingdom)
Mr James Shipley (Quintus Technologies AB, Sweden)
The encapsulation and HIP technology has developed over the years to become a high-performance, high-quality and cost-effective process for the manufacture of a wide range of components such as simple shape billets for the machining of high performance PM HSS cutting tools, and the manufacture of large near net shape stainless parts for the oil and gas industry. The versatility and flexibility of the HIP process, combined with superior material properties, make it an ideal choice for new applications, among other powder metallurgy technologies.
This Special Interest Seminar continues to focus on Ni-base super alloys for powder metallurgical applications, with particular interest in AM produced parts, and the effect of microstructure and mechanical properties of some original applications of Hot Isostatic Pressing technology.
Hot Isostatic Pressing of AM Materials: Case Studies Results
Mr James Sears (Carpenter Technology Corporation, USA)
Hot Isostatic Pressing (HIP) has been used for years in the densification of casing mainly to heal defects. The use of HIP for AM materials produced by Powder Bed Fusion is for a similar reasons but also offers some additional benefits by reducing anisotropic behavior and providing some compressive strain to the parts produced. HIP is also being used in conjunction with binder-jet technology as a final step after sintering to help obtain higher density is the final product. Case studies based laser powder bed fusion of 718 Ti-6-4 and CCM alloys will be provided.
Removal of AM Processing Defects and Improving Material Properties in Ti6AI4V
Dr Kathrin Horenkamp (Bodycote, UK)
When making parts via the additive manufacturing process, even with the most robust processing techniques the powder bed additive process may still create small defects during the build cycle. Several investigational sample sets were manufactured via EB powder bed additive manufacturing. The sample sets contained purposely designed defects that mimic defects that might normally be found in components built via powder bed processing techniques. The investigation compares the effect of post build thermal processing (Hot isostatic Pressing and heat treatments) against as built properties. Mechanical testing data is reported to show the improved material properties by post build thermal processing. Metallography data is reported to show that post build thermal processing conclusively reduces the number and size of the defects, if not eliminating them entirely.
Microstructural design of Ni base superalloys by HIP and its benefit
Dr Inmaculada Lopez-Galilea (Ruhr University Bochum, Germany)
Single crystal Ni-base Superalloys (SXs), used as blade materials, operate at temperatures close to their melting point and have to withstand mechanical and chemical degradation. Casting and extensive solution heat-treatments of such blades introduce porosity, which can only be reduced by hot isostatic pressing (HIP). Recent developments of a HIP unit with a quenching possibility allow performing heat treatments and eliminate porosity simultaneously (integrated HIP treatment). This work gives an overview about the opportunities that such a unique HIP offers for the solution heat-treatment of conventionally cast SXs or directionally solidified Ni-base superalloys fabricated by selective electron beam melting (SEBM).
The influence of temperature, pressure, and cooling method on the evolution of γ/γ'-morphology and on the pore shrinkage is investigated. The cooling method has a strong impact on the γ'-particle size and shape. Slow or natural cooling lead to coarse γ'-precipitate sizes. Quenching after solutioning at 100 MPa leads to a high number density of small γ'-particles, ideal for the subsequent formation of a fine and uniform γ/γ'-microstructure after ageing. Porosity reduction was most efficient at T>Tγ'-solvus. Based on these findings, first, an integrated solution and aging heat treatment for an as-cast SXs is implemented into the HIP unit. Second, short HIP treatments are applied on SEBM parts, generating promising and defect free microstructures. Finally, a HIP treatment is satisfactorily used to rejuvenate the γ/γ'-microstructure of SXs after creep degradation, re-establishing the γ/γ'-microstructure without recrystallization and closing all pores and creep cavities.