Fabrication of Dense, Near Net-Shaped W/ZrC Composites by the PRIMA-DCP Process

Abstract

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the i gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments ret " . j o of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE ^DD-yW SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)USAF/AFRL AFOSR 801 N. Randolph Street ArlingVA 22203 SPONSOR/MONITOR'S ACRONYM(S) AFOSR SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTDistribution Statement A. Approved for public release; distribution is unlimited. The fundamental conversion mechanism for the following net liquid/solid displacement reaction has been examined: (Zr) + WC(s)=ZrC(s)+W(s) (1) where (Zr) refers to zirconium dissolved within a Zr-Cu melt. Such mechanistic knowledge is needed in order to be able to predict die time required, under various processing conditions, for full conversion of porous WC performs into dense ZrC/W composites (e.g., for rocket nozzle applications) by die DCP method. For this fundamental study, dense wafer of WC were prepared by hot isostatic pressing at 1850oC. The wafers were then unmersed in a vertical orientation in a Zr-Cu melt at temperatures in die range of 1150-1400oC for times up to 24 hours. After such exposure, the polished WC surfaces were found to be coated with two reaction product layers. A layer of tungsten was observed to be in direct contact with the WC. A second, external layer of ZrC separated die W layer from die melt. The diicknesses of die W and ZrC layers were found to: i) increase at a parabolic rate with time, ii) be independent of the relative vertical position on the WC surface, and iii) increase Objective: This project has been focused on developing a better understanding of the fundamental kinetic mechanism(s) (i.e., rate-limiting step(s), kinetic rate law(s)) of the DCP (Displacive Compensation of Porosity) process for fabricating ZrCAV composites. Approach and Key Results:The fundamental conversion mechanism for the following net liquid/solid displacement reaction has been examined:where (Zr) refers to zirconium dissolved within a Zr-Cu melt. Such mechanistic knowledge is needed in order to be able to predict the time required, under various processing conditions, for full conversion of porous WC preforms into dense ZrCAV composites (e.g., for rocket nozzle applications) by the DCP method. For this fundamental study, dense wafers of WC were prepared by hot isostatic pressing at 1850°C. The wafers were then...