Mechanical Milling Process as Severe Plastic Deformation Method

Abstract

Synopsis :Mechanical milling is one of the severe plastic deformation processes and can give a heavy deformation to a metallic powder. Using such a mechanical milling process nano crystalline material can be produced with relatively simple equipment, low cost and short time. The mechanical milling process leads to finer grain than other severe plastic deformation for bulk materials and the grain size produced by mechanical milling is less than 10 nm. Nano grain structure by mechanical milling is finally formed with nano layered structure though the grain refinement rate depends on the milling method and the milling condition. The minimum grain size produced by mechanical milling is related to many factors such as melting point and stacking fault energy. The nano grain tungsten powder demonstrates a good workability and its sintered compact demonstrates the superplastic deformation at 1473K. When the milling intensity is suitable, mechanically milled powder consisting of shell and core can be produced. The compacts produced from such mechanically milled powder have the nano / meso hybrid microstructure and demonstrate advanced mechanical properties.

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

“…In order to avoid contamination caused by the milling media, conventional CP titanium powder with average particle size of 45 mm was milled for 86.4 ks to make a titanium-coating-layer on the surface of both vial and balls. 19) Furthermore, no process agent was used during the milling. The milling intensity can be controlled by selecting the ball-to-powder weight ratio and process time.…”

“…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.…”

Effects of Microstructure on Mechanical Properties of Harmonic Structure Designed Pure Ni

“…Therefore, the sintering of longtime MM powder ultimately leads to the Ni sintered compacts with approximately uniform fine-grained microstructure matrix as similar to the fine-grained conventional homogeneous microstructured Ni compact. 8,12,13) 3.2 Mechanical properties of harmonic structured Ni Figure 6 shows typical nominal stress-strain diagram obtained by tensile tests of (a): Harmonic Structured Ni compacts (HS, XZ) and (b): Homogeneous Structure Ni compacts (Homo, AD). For the HS Ni compacts, both Yield strength (YS) and Ultimate Tensile Strength (UTS) increased ( Fig.…”

Harmonic Structure Design: A Strategy for Outstanding Mechanical Properties in Structural Materials

“…Recently, Ameyama et al proposed a novel concept of "harmonic structure" (HS) design, consisting of a specific spatial distribution of ultra-fine grains (UFG) and coarse grains (CG), that is, the CG areas (core) surrounded by three-dimensionally (3D) continuously connected network of UFG areas (shell) [23][24][25][26][27][28][29][30][31]. Owing to its unique topological 3D gradient structure, the harmonic-structured materials were reported to exhibit high work hardening that extends to higher strain regions, leading to delay in the initiation of plastic instability.…”

“…Owing to its unique topological 3D gradient structure, the harmonic-structured materials were reported to exhibit high work hardening that extends to higher strain regions, leading to delay in the initiation of plastic instability. Consequently, a good combination of high strength and high ductility can be achieved [29][30][31].…”