Development and Optimization of Rolled Product Forms Using Blended-Elemental Powder-Based Ti-6AL-4V Alloy

The feasibility of rolling process development has been successfully demonstrated at RTI International Metals, Inc. in ambient environment using initial rolling preforms of blended-elemental hydrided titanium powder billets fabricated by ADMA using their titanium hydride-powder blended with master alloy aiming at Ti-6AL-4V composition, followed by direct-consolidation by cold isostatic pressing (CIP), and vacuum sintering.  All elements in the pre-rolling billet preforms including aluminum, vanadium, oxygen, hydrogen, carbon, and nitrogen were within the AMS Specification limits.  Measurements of tensile properties of the plate and sheet rolled billets using processing pathways initially in the beta then in the alpha-beta ranges of temperature, showed equivalent or superior tensile properties as compared to rolling processed wrought ingot-based Ti-6AL-4V billet materials.  While the rolling processing development for Boeing at RTI is currently aimed at meeting the generic rolling product Specifications, such as AMS 4904D, and/or ASTM B267-07, the successful rolling processing development at RTI was enabled by rolling process modeling and a workability study at RTI, in addition to a preceding ADMA optimization of their fabricated pre-rolling billets, focusing on the CIP-and-sintering steps for reducing both oxygen and residual hydrogen contents to levels at or below the AMS Specification limits for Ti-6Al-4V composition.  The goal of the optimization steps both at ADMA and RTI is to provide the best property balance of the blended-elemental powder-based rolled products spanning both plate and sheet ranges of thicknesses, while minimizing the required number of rolling passes from initial consolidated billet thicknesses as near as possible to the final product thickness which provides just enough thermomechanical working of the powder-based billet to meet the Boeing-approved aerospace product specifications in terms of chemistry, microstructure and properties.  The Boeing-executed test matrix included processing-microstructure-property correlations of tensile properties, S-N fatigue life, fatigue crack growth rate da/dN, fracture toughness per ASTM-E399-K_IC (K_Q), and stress-corrosion resistance as measured by the NACE-K_ISCC test TM0177, and/or the bolt-loaded ASTM G-168 standards.  This paper examines correlations between powder-based, and ingot-based rolled products in terms of meeting AMS Specification requirements.