Fracture Behavior of W-Ni-Fe Heavy Alloys
- PDF / 2,263,379 Bytes
- 8 Pages / 594 x 774 pts Page_size
- 85 Downloads / 250 Views
I.
INTRODUCTION
THE heavy
alloys constitute several tungsten based two phase composites which rely on various Cu, Ni, or Fe additions to form a ductile matrix. These alloys are used in diverse applications ranging from radiation shields to counter balances. Recent strong attention has been focused on the mechanical properties of these alloys and the observed sensitivity in ductility. There are two general goals in current research with heavy alloys: (1) improve the overall properties (higher strength, ductility, and toughness), and (2) isolate and avoid the causes of embrittlement. As the tungsten content increases, the density of the alloy increases. Additionally, the material decreases in ductility and has a greater sensitivity to sources of embrittlement. There are several variables which influence the mechanical properties of heavy alloys. This list includes the impurities, sintering conditions, post-sintering treatments, and the testing conditions. Recent findings have been somewhat contradictory in that the causes of embrittlement have been given as intermetallic phase formation, impurity segregation, hydrogen embrittlement, shrinkage pore formation, and a varying ductile-brittle transition temperature. Edmonds and Jones 1 found intermetallic phase formation at the matrix tungsten interface in a 90W-5Ni-5Fe alloy and gave this as a cause for embrittlement. This has also been suggested as the cause of embrittlement in slow cooled alloys with a Ni: Fe ratio of 7 : 3.2'3 However, Henig, e t a l . 4 claim no detrimental effect from this intermetallic. Other investigators5 have been unable to confirm the existence of this phase in embrittled material with a 1 : 1 ratio of Ni: Fe. Several reports 1'6-8have shown a strong impurity influence, wherein the elements such as P and S segregate to the tungsten-matrix interface during slow cooling from elevated temperatures (over approximately 800 ~ Yoon e t a l . 9 and others ~~ found strength and ductility degraded by heating in a hydrogen atmosphere. The effect of hydrogen is to weaken the tungsten-matrix interface. Kang e t a l . ~2 have shown mechanical property decrements due to rapid cooling K. S. CHURN, formerly a Postdoctoral Fellow at RPI under a fellowship from the Korea Science and Engineering Foundation, is now Systems Manager at the Daejeon Machinery Depot, Daejeon, Korea. R.M. GERMAN is Associate Professor, Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12181. Manuscript submitted April 15, 1983. METALLURGICALTRANSACTIONS A
from the sintering temperature. The formation of matrix phase solidification porosity with rapid cooling is quite detrimental to the properties; Chum and Yoon 13have given a clear demonstration of the porosity effect. The fracture behavior of the tungsten heavy metals has been explored by several investigators. Krock and Shepard 14 proposed that crack initiation was at the grain surface, while crack growth is governed by the matrix phase. Several other investigations 13'~5-2~have observed preferential crac
Data Loading...
