Thomas R Muth

Current Status of Ti PM: Progress, Opportunities and Challenges

Utilization of titanium components made by powder metallurgy methods has had limited acceptance largely due to the high cost of titanium (Ti) powder. There has been renewed interest in lower cost economical powders and several Ti reduction methods that produce a particulate product show promise. This talk summarizes work done at Oak Ridge National Laboratory to consolidate these economical powders into mill products. Press and sinter consolidation, hot isostatic pressing (HIP) and direct roll consolidation to make sheet have been explored. The characteristics of the consolidated products will be described as a function of the consolidation parameters.

Mesoscale Modeling and Validation of Texture Evolution during Asymmetric Rolling and Static Recrystallization of Magnesium Alloy AZ31B

The focus of the present research is to develop an integrated deformation and recrystallization model for magnesium alloys at the microstructural length scale. It is known that in magnesium alloys nucleation of recrystallized grains occurs at various microstructural inhomogeneities such as twins and localized deformation bands. However, models need to be developed that can predict the evolution of the grain structure and texture developed during recrystallization and grain growth, especially when the deformation process follows a complicated deformation path such as in asymmetric rolling. The deformation model is based on a crystal plasticity approach implemented at the length scale of the microstructure that includes deformation mechanisms based on dislocation slip and twinning. The recrystallization simulation is based on a Monte Carlo technique that operates on the output of the deformation simulations. The nucleation criterion during recrystallization is based on the local stored energy, and the Monte Carlo technique is used to simulate the growth of the nuclei resulting from local stored energy differences and curvature. The model predictions are compared with experimental data obtained through electron backscatter analysis and neutron diffraction.

Shear Rolling of Magnesium Sheet for Automotive, Defense, and Energy Applications

Magnesium is the lightest structural metal known: at approximately 1/5 the density of steel, 1/2 the density of titanium and 2/3 the density of aluminum. Hence magnesium alloys represent potential weight savings across the entire transportation industry. The major hurdle to the deployment of magnesium products by the transportation industry is the price barrier that exists due to the current high cost of producing magnesium alloy sheet on a volume basis. Proven technology (e.g., twin roll sheet casting and hot reversing coil mill technology) exists which could lower the cost of magnesium alloy sheet by as much as 50%, but needs to be demonstrated and implemented in high volume production to achieve benefits. In addition, the predominant basal texture (alignment of basal planes parallel to the sheet surface) that exists in magnesium alloy sheet results in poor low temperature formability resulting in added fabrication costs. Cost reduction achieved through energy efficiency, coupled with even greater energy savings by deployment of this lightest of metals, will help the United States achieve its goal to eliminate dependence on foreign fossil fuel. Oak Ridge National Laboratory (ORNL), Magnesium Elektron North America (MENA), and FATA Hunter collaborated on this project to develop shear rolling technology of magnesium sheet to enable improvement of the formability of magnesium sheet while addressing cost and lower energy consumption.

Production of wide shear-rolled magnesium sheet for part forming

In recent years the process of shear rolling has seen considerable study, particularly for heavily textured materials such as magnesium. The goal of this work has been to produce sheet with greater formability for industries such as automotive and aerospace. To date, almost all work on asymmetric rolling has been carried out on small strips that are not large enough to produce parts. The current work will discuss scaling-up of the shear rolling process to generate wider sheet. A mill at the Magnesium Elektron North America plant was modified to allow shear rolling at a ratio of 1:1.35 on sheets up to 36” wide. AZ31B and ZEK100 sheets of size 36”x72” were shear rolled and demonstration automotive parts have been formed by Superform USA.

The Effect of Rare Earth Elements on the Texture and Formability of Shear Rolled Magnesium Sheet

The lower relative formability of magnesium alloy sheet can be a restrictive factor when designing light weight engineering structures. Standard symmetric rolling introduces a strong basal texture that decreases the formability; however, asymmetric rolling has been put forward as a possible route to produce sheet with weaker basal texture and greater ductility. It has also been shown in recent work that weaker textures can be produced through the addition of rare earth elements to magnesium alloys. Therefore, this study has been carried out to investigate the effect of rare earth additions on the texture changes during asymmetric rolling. Two alloys have been studied (AZ31B and ZEK100), in which a significant difference is the presence of rare earths in the ZEK100 but not in AZ31B. The differences in texture, microstructure and mechanical properties will be discussed.

Aircraft Propeller Hub Repair

The team performed a literature review, conducted residual stress measurements, performed failure analysis, and demonstrated a solid state additive manufacturing repair technique on samples removed from a scrapped propeller hub. The team evaluated multiple options for hub repair that included existing metal buildup technologies that the Federal Aviation Administration (FAA) has already embraced, such as cold spray, high velocity oxy-fuel deposition (HVOF), and plasma spray. In addition the team helped Piedmont Propulsion Systems, LLC (PPS) evaluate three potential solutions that could be deployed at different stages in the life cycle of aluminum alloy hubs, in addition to the conventional spray coating method for repair. For new hubs, a machining practice to prevent fretting with the steel drive shaft was recommended. For hubs that were refurbished with some material remaining above the minimal material condition (MMC), a silver interface applied by an electromagnetic pulse additive manufacturing method was recommended. For hubs that were at or below the MMC, a solid state additive manufacturing technique using ultrasonic welding (UW) of thin layers of 7075 aluminum to the hub interface was recommended. A cladding demonstration using the UW technique achieved mechanical bonding of the layers showing promise as a viable repair method.

Production of Diesel Engine Turbocharger Turbine from Low Cost Titanium Powder

Turbochargers in commercial turbo-diesel engines are multi-material systems where usually the compressor rotor is made of aluminum or titanium based material and the turbine rotor is made of either a nickel based superalloy or titanium, designed to operate under the harsh exhaust gas conditions. The use of cast titanium in the turbine section has been used by Cummins Turbo Technologies since 1997. Having the benefit of a lower mass than the superalloy based turbines; higher turbine speeds in a more compact design can be achieved with titanium. In an effort to improve the cost model, and develop an industrial supply of titanium componentry that is more stable than the traditional aerospace based supply chain, the Contractor has developed component manufacturing schemes that use economical Armstrong titanium and titanium alloy powders and MgR-HDH powders. Those manufacturing schemes can be applied to compressor and turbine rotor components for diesel engine applications with the potential of providing a reliable supply of titanium componentry with a cost and performance advantage over cast titanium.