Aerospace Titanium Alloy Melt Process Quality Improvements

Abstract

This Jet Engine Titanium Quality Committee (JETQC) paper describes industry quality improvements since 1990. Quality refers to freedom from melt-related hard-alpha and high-density inclusions (HDI). JETQC, formed under the auspices of the U.S. Federal Aviation Administration (FAA) following the Sioux City aircraft accident in 1989, is comprised of U.S., E.U. and Japanese aircraft engine manufacturers to address the quality of premium / rotor quality titanium alloy production. Titanium suppliers provide melt-related inclusion data. JETQC focuses on hard-alpha and HDI inclusion rates in premium quality (PQ) titanium alloy products for critical rotating aircraft engine applications. PQ materials typically are produced via triple vacuum arc re-melt (3XVAR) or hearth melt VAR (HMVAR) processes, but more recently, the Skull plus VAR (SVAR) process has been introduced. Hard-alpha rates have continued to decline over the last decade primarily for the HMVAR process. HDI rates declined in the early 90’s, but more recently the overall rate has stayed approximately constant with inclusions confined to the 3XVAR process. Combining the trends for both hard-alpha and HDIs, the HMVAR process has demonstrated in recent years to be higher quality compared with the 3XVAR process.