Nano Grain Formation in Tungsten by Severe Plastic Deformation-Mechanical Milling Process

Abstract

The mechanism of nano grain formation in tungsten by mechanical milling, which is one of the methods for severe plastic deformation, was investigated. The powder microstructure was divided in some layered grain structures, and finally consisted of equiaxed nano grains. This nano grain structure was formed by the subdivision of the layered grain. These nano grains have non-equilibrium grain boundary structure. It is considered that such a specific microstructure is formed by extremely heavy plastic deformation by due to the mechanical milling process.

New Microstructure Design for Commercially Pure Titanium with Outstanding Mechanical Properties by Mechanical Milling and Hot Roll Sintering

“…The present authors have previously reported that the formatting of equiaxed nano grain structure in MM powder occurs because of the grain sub-division and rotation of those elongated grains. [12][13][14][19][20][21][22] Not only titanium, but also copper, 20) iron, 20) nickel, 21) tungsten 19,22) and austenitic stainless steel [12][13][14]19,21) powder demonstrate almost the same equiaxed nano grain structure after the mechanical milling process. Formation of the nano grains depends on the stacking fault energy since dislocation accumulation by milling is extremely important for the grain sub-division.…”

Al Alloy Nanocomposite Reinforced with Physically Functionalized Carbon Nanotubes Synthesized via Spark Plasma Sintering

“…The ball milled powders exhibit flat and flaky shape with a wide size range of 2-40 µm, whereas particle sizes of the as received powder was 2-10 µm. This variation in the size of the ball-milled powder particles is attributed to the wide variation in initial particle size [14]. Formation of nano sized grains in ball milled powders has been endorsed by the X-ray diffraction result as shown in Fig.…”

“…The heavy plastic deformation of the Al-Si powder particles led to work hardening resulting in fracture and thus the creation of new particle surface, enabling the particle to weld together and increase the particles size. But as the deformation proceeded, the particles were again work hardened and fragmented to flakes by a fatigue failure mechanism [14]. Eventually, formation of flaky Al-Si powders occurred with a size reduction and wide size variation (Fig.…”

“…Heavy plastic deformation of the Al-Si powders took place during high-energy ball milling which resulted in the generation of dislocations in large numbers in the grains [12,13]. Due to generation and rearrangement of dislocations during the milling, grain refinement occurs due to the formation of sub-grains, which subsequently turned out to be grains in the submicron and nano-size range sub-micron and nanocrystalline grains [14]. Elastic modulus and microhardness of the NCs have been tabulated in Table 1 …”

Synthesis of nanocrystalline tungsten and tungsten carbide powders in a single step via thermal plasma technique

“…Over the past few decades, several processes like wire explosion [9], ball milling [10,11], chemical vapor synthesis [12], plasma synthesis [5,6] etc. were developed to synthesize nano size tungsten powder.…”