Past, Present, and Future Developments of Tungsten 25 Rhenium Tool Material for Friction Stir Welding of Steel and Hard Metals

摘要

Rhenium Alloys Inc (RAI) was introduced to the Friction Stir Welding (FSW) process by The Welding Institute (TWI) in early 1999, with the application of FSW of commercially pure titanium. At that time, RAI only produced tungsten 25-26% rhenium (W25-26%Re) wire at (.25-.5mm) diameter for type C and D thermocouple wire. RAI began its next phase of development in the early 2000s with an introduction into the Dual Use Science and Technology (DUST) program, which applied FSW process to HSLA65 steel. RAI was brought into the program by the MTS Corporation to use W25%Re to demonstrate the use of a tungsten-based alloy for FSW. On the DUST Program, W25%Re was used to join a test article to demonstrate the use of FSW for marine applications. Extensive characterization was performed on the W25%Re and the FSW welds. The W25%Re rods initial use on the DUST program were produced by the wire bar process. This process did not produce a dense rod for the FSW process, so RAI scaled up the production to produce dense, large diameter W25%Re rods. Increasing the diameter from a wire bar to large diameter W25%Re rod was a difficult process, due to the limitations posed by a lack of adequate equipment to process large diameter W25%Re rods. In 2005, RAI obtained ultra high temperature sintering facilities, which significantly increased the density and properties of W25%Re rods. Subsequently, RAI acquired both large-scale powder compaction capabilities and rotary swaging faculties, in addition to the recently acquired sintering capabilities. These facilities significantly enhanced the capabilities to produce 100% dense rods with worked structures. RAI then undertook an extensive research program in late 2007 to investigate the processes and properties of W25%Re and W25%Re with the addition of hafnium carbide (HfC). Microstructures and mechanical properties were examined for the two alloy compositions at three differing testing temperatures (21°C, 1371°C, and 1926°C). In early 2001, EWI ramped up its efforts in the area of welding hard metals with FSW. Initial investigations used commercially pure tungsten alloys as FSW tool materials. Working as a participant on a Metals Affordability Initiative (MAI) early in the 2000's, EWI began working with various tungsten alloys for welding titanium, which were then extended to other hard metals. In late 2005, EWI started modeling the W25%Re for joining steel using the FSW process based on the property data produced by RAI. That model was used to develop the Variable Penetration Tool (VPT) designs, which were used in conjunction with tungsten-based alloys for welding steels and other hard metals. Today, RAI has acquired both the extrusion and forging capabilities to produce large diameter FSW refractory metal rods and FSW tools that have customized mechanical properties to meet the demand application. RAI is moving from a manufacturer of raw material to a manufacturer of refractory metal FSW tools, with EWI as its technology collaborator. The demand for joining thicker and thicker sections continues to grow. RAI must be able to produce tools and tool material in increasingly larger diameters. The refractory metal FSW tool material must withstand softening at elevated temperatures without significant wearing issues or catastrophic failure during FSW. In the future, the EWI- RAI collaboration will be improving the FSW tool materials and designs for welding, steel, titanium, and nickel (Ni) based superalloys, with a low cost, long lasting tool tailored to meet the requirements of future demands.