The production of W-0.35HfC (Mol %) wirebar by arc melting and high energy rate extrusion of small diameter ingots

Tungsten alloy fiber reinforced tungsten is a candidate emitter material for space nuclear thermionic multi-kilowatt power systems. Fuel swelling which results in emitter deformation has been a primary concern for being able to achieve long lived (7 years or greater) thermionic fuel elements (TFE) operating at temperatures at or above 1900 K. The tungsten alloy (W-0.35 mo/%HfC) has extremely attractive mechanical properties above 1900 K and is a candidate reinforcement of tungsten for emitters. Because of its high strength, processing of the W-035HfC alloy to small diameter (0.38mm) wire has been difficult and the yield of useable product has been low. The purpose of this work was to demonstrate that by vacuum arc melting 38mm diameter ingots and high energy rate extrusions, small diameter (18mm) rod could be produced which is more compatible with swaging equipment used in tungsten wire production. Six 38 mm diameter ingots of W-0.35 HfC were produced by consumable electrode vacuum arc melting. The ingots were clad in 46 mm diameter molybdenum heated to 2270K and successfully extruded through a zirconia coated die at a reduction ratio of 7:1. The microstructure of the as-extruded bars is highly worked and should be amenable to processing to small diameter wire