Enhanced Performance Near Net Shape Titanium Alloys by Thermohydrogen Processing

Abstract

Public Reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other documentation. This is a final report and it covers the work reported in interim reports and work done during this calendar year. This research program was aimed at a detailed understanding of the effect of hydrogen as a temporary alloying element (thermohydrogen processing, THP) on processing parameters, microstructural modifications and final mechanical properties of castand-wrought (ingot metallurgy), powder metallurgy and cast titanium alloys. Fundamental results have been obtained which can now be used to develop optimum THP steps to refine the microstructure and improve the mechanical properties of titanium alloys. As a part of this project, the phase diagram of the Ti-6AI-4V -hydrogen system, and a determination of the stable and metastable phases, which occur in this system, have been defined. Kinetics of the ß phase decomposition has been studied and the non-equilibrium TTT (temperature-time-transformation) diagrams of the beta to alpha+beta+hydride transformation have been determined for the alloys with 10, 20, and 30 at.% hydrogen. Kinetics of decomposition of martensite structures have also been determined for these three hydrogen concentrations. The results have been presented at international meetings, twenty-two technical papers were published and twelve papers have been submitted for publication. Additionally a patent was also awarded. The results of the work have been transitioned to an Army SBIR program designed to produce low cost titanium components for armored vehicles. ABSTRACT This research program was aimed at a detailed understanding of the effect of hydrogen as a temporary alloying element (thermohydrogen processing, THP) on processing parameters, microstructural modifications and final mechanical properties of castand-wrought (ingot metallurgy), powder metallurgy and cast titanium alloys. Fundamental results have been obtained which can now be used to develop optimum THP steps to refine the microstructure and improve the mechanical properties of titanium alloys. As a part of this project, the phase diagram of the Ti-6AI-4V -hydrogen system, and a determination of the stable and metastable phases, which occur in this system, have been defined. Kinetics of the ß phase decomposition has been...

An experimental study of the (Ti–6Al–4V)–xH phase diagram using in situ synchrotron XRD and TGA/DSC techniques

“…In the early 1980s, Kerr et al reported fine microstructures produced via THP and conducted a comprehensive study on the effects of processing parameters on the final microstructure and tensile properties [11,12]. Subsequently, the THP process was investigated extensively for both wrought Ti and powder metallurgy (PM) Ti [13][14][15][16][17][18][19][20][21][22][23][24].…”

Hydrogen as a temporary alloying element in titanium alloys: thermohydrogen processing

“…Recently, an increased understanding of titanium metallurgy has demonstrated that, when used correctly, hydrogen as a temporary alloying element can become a powerful tool in improving processing and microstructure/mechanical properties of titanium alloys. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] This so called thermohydrogen processing (THP) is based on the modifying effect of hydrogen as an alloying element on phase compositions, development of metastable phases, and kinetics of phase transformations in titanium alloys. 7 In this approach, the high diffusivity of hydrogen in titanium is used to first add hydrogen to the alloy by controlled diffusion from a hydrogen environment and then, after processing, to remove it by a controlled vacuum anneal.…”