Mechanical alloying (alloy formation by friction welding) using a powder of the high temperature nickel alloy NiCr13MoAL with 3% ThO2

The process of mechanical alloying was investigated using a powder of the high temperature nickel alloy NiCr13MoAl containing 3 vol.% ThO2. The original material consisted of nickel and chromium powder, two powdered master alloys containing the elements aluminium, titanium, niobium, and molybdenum, which have an affinity for oxygen, as well as a nickel powder enriched with fine thorium oxide. The mixed starting powder was dry-milled up to 40 hr. in an Attritor and specimens taken during milling. These were examined in several ways. The experimental results verified that mechanical alloying consists of alternating fragmentation and rewelding. The necessary innumerable friction welds are associated with formation of solid solutions in small regions of the lattice - which in large numbers lead to the formation of a homogenous alloy. The homogenisation increases with increasing milling time with the most significant changes occurring in the first 10 hours. The results also indicated that chromium should be added in a master alloy. Under the experimental conditions selected, a milling time of 40 hr. was completely adequate for the uniform distribution of the alloying elements, considering the subsequent processing to a high temperature material by hot extrusion or hot isostatic compression. The term 'mechanical alloying' is also completely justified as the innumerable friction welds lead to an almost uniform distribution of the alloying components by formation of a solid solution. (orig.)