effects of hydrogen on low temperature hardening and embrittlement of V-Cr alloys
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1.
INTRODUCTION
RECENTLY, there has been a renewed interest in refractory metal alloys, particularly V-based alloys, as possible candidates for first wall materials in controlled fusion reactors. Vanadium alloys can provide lower thermal stresses for a given flux, easy fabrication, excellent mechanical properties at elevated temperatures, and offer good resistance to radiation damage. On the other hand, there is some concern about the effects of the light interstitial elements (C, N, O, and H) on the mechanical properties of refractory alloys. Hydrogen embrittlement of vanadium alloys, for example, is not expected in fusion reactors but is possible since hydrogen and its isotopes are always present in such reactors. Much of the mechanical property data for V-Cr alloys is documented in a review article by Harrod and Gold ~ and is confined to room temperature measurements. More recently Iwao et al. 2 reported on the mechanical properties of V-Cr alloys between room temperature and 1273 K, but to the authors' knowledge little or no attention has been given to the effect of interstitial elements on these properties at any temperature. The purpose of the present paper is to examine the effects of hydrogen on the mechanical properties of selected V-Cr alloys at low temperature and to characterize any embrittlement found. Similar investigations of hydrogenated V-Nb 3 and V-Ti 4 alloys yielded results compatible to those to be presented here, and some direct comparisons between the V-Cr and V-Ti systems are made.
II.
M A T E R I A L S AND P R O C E D U R E S
The V used in this investigation came from two different sources. Double-electrorefined material was purchased from the United States Bureau of Mines and consumable arc-melted V was obtained from Wah Chang, Albany. The iodide Cr employed as the alloying component was purchased from the Chromaloy Corporation. Alloys containing 10 and 20 at. pct Cr were prepared from the electrorefined V while the pure V ingot as well as the 2.5 and 5 at. pct Cr
C.V. OWEN, Associate Metallurgist, and W . A . SPITZIG and O. BUCK, Senior Metallurgists, are with Ames Laboratory, Iowa State University, Ames, IA 50011. Manuscript submitted November 4, 1986. METALLURGICAL TRANSACTIONS A
alloy ingots were prepared using the Wah Chang material. All of the ingots were in the form of "fingers" and were prepared by arc-melting under purified argon. Chemical analyses from both ends of each alloy ingot showed that the actual and intended compositions were nearly the same. The 14 mm diameter alloy ingots were encapsulated in stainless steel and reduced by swaging to a diameter of 6.35 mm. Swaging temperature was 1123 K for the V2.5Cr, V-5Cr, and V-10Cr ingots, and 1173 K for the V20Cr alloy. After de-jacketing both the V-2.5Cr and V-5Cr alloys were reduced to a final diameter of 2.54 m m by swaging at room temperature with intermediate vacuum annealing at 1123 K. The V-10Cr and V-20Cr alloys were re-jacketed and reduced further by hot swaging at the appropriate temperatures to a diameter of 3.8
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