Innovative Manufacturing Process Improvements: HIP Process Model

The Missile Defense Agency (MDA) and other components of the Department of Defense (DOD) are cur-rently developing advanced materials for propulsion hardware, weapons systems, thermal management applications, and divert and altitude control systems (DACS). The materials include high temperature metals, ceramics, metal matrix composites, and refractory carbides and borides. Several of these materials are made by hot isostatic pressing (HIPping). In the HIP process a near net shape billet is molded and encapsulated in a metal can. The can is evacu-ated and exposed to a high temperature while under uniform, high external pressure. The HIP process eliminates internal voids as the billet is consolidated, resulting in a material that is nearly 100% dense and exhibits a uniform fine-grained microstructure. The resulting material possesses high strength, ductility and fatigue resistance. Many variables affect the results of the HIPping process including: billet material, billet density, billet mi-crostructure, impurities, component geometry, can material, can geometry, weld integrity, evacuation, seal, tempera-ture history and pressure history. To date, many of these parameters have been arrived at through an Edisonian process know in the industry as, "heat `em and beat `em." While the results have led to a very useful method for manufacturing high strength material, the development process has been costly since several blind alleys must be tried before a successful fabrication path is defined. The proposed program seeks to improve the process by developing a thermostructural model of the HIP-ping process. The model can be used to guide the design of the HIP hardware and the selection of the processing parameters. Specifically, the model seeks to answer several questions critical to the HIP process: 1) Will the can survive? 2) Will the billet consolidate? 3) Will the microstructure be acceptable? 4) Will the final dimensions be acceptable? The program will be undertaken by the team of Materials Research & Design and Exothermics. MR&D is well known in the advanced materials community for its expertise in the design of components for extreme environments. Exothermics is expert at HIPping unique materials such as titanium carbide sputtering targets and hafnium nitride rocket motor throats. The program consists of six tasks including: 1) Literature review, 2) Constitutive model de-velopment, 3) Thermostructural modeling, 4) Trial fabrication, 5) Characterization, and 6) Correlation. The test of feasibility in the Phase I program will be the comparison of model predictions of billet behavior with measured data from the fabrication and characterization tasks.