Study on the combination of cobalt-based superalloy and ferrous alloys by bimetal-layer surfacing technology in refabrication of large hot forging dies
“…The crystal structure and the orientation relationship were a typical and the priority precipitated phases occurred along {001} α when the 7055 aluminium alloy was subjected to the T6 heat treatment for 4 h, see Figure 5. When the aging time was lengthened to 12 h, the particle distribution was uneven, and many dispersion regions and mixture regions of the dispersions were observed along {001} α in the cutting surface metal after HSC [25]. Figure 5 Microstructure and crystal orientation of the 7055 aluminium alloy after the T6 treatment.…”
The following paper examined changes in the microstructure of 7055 aluminium alloy before and after high-speed cutting (HSC) were examined, for various (T6, T7, and T84) heat treatment conditions. In the T6 state, the results demonstrated that the number of η″ particles gradually reduced and there was pinning in the η″ particles. After both the T7 and T84 heat treatments, a dislocation was observed in the microstructure by transmission electron microscopy. Grain boundaries in the T6 state were continuous with no obvious non-precipitate zone before HSC. The grain boundary width in the T7 state before HSC was double the T6 value. The grain boundary width for the T84 state alloy was similar to that in the T7 state, but less clearly defined. This is part of a thematic issue on Small Scale Mechanics - EUROMAT.
“…The crystal structure and the orientation relationship were a typical and the priority precipitated phases occurred along {001} α when the 7055 aluminium alloy was subjected to the T6 heat treatment for 4 h, see Figure 5. When the aging time was lengthened to 12 h, the particle distribution was uneven, and many dispersion regions and mixture regions of the dispersions were observed along {001} α in the cutting surface metal after HSC [25]. Figure 5 Microstructure and crystal orientation of the 7055 aluminium alloy after the T6 treatment.…”
The following paper examined changes in the microstructure of 7055 aluminium alloy before and after high-speed cutting (HSC) were examined, for various (T6, T7, and T84) heat treatment conditions. In the T6 state, the results demonstrated that the number of η″ particles gradually reduced and there was pinning in the η″ particles. After both the T7 and T84 heat treatments, a dislocation was observed in the microstructure by transmission electron microscopy. Grain boundaries in the T6 state were continuous with no obvious non-precipitate zone before HSC. The grain boundary width in the T7 state before HSC was double the T6 value. The grain boundary width for the T84 state alloy was similar to that in the T7 state, but less clearly defined. This is part of a thematic issue on Small Scale Mechanics - EUROMAT.
“…Some researcher has claimed that the thickness of the layer produced by this technology is two times larger than that produced by plasma nitriding [84]. In recent years, an experimental studies of Shen L and his colleagues [85] showed the combination of this technology with other methods to obtain maximum hardness. The results showed an increase of 400 HV in hardness.…”
“…where x i ðkÞ is the normalized value, miny i ðkÞ and maxy i ðkÞ denote the smallest value and largest value of the y i ðkÞ for the i quality characteristics, respectively. Next, the grey relation coefficient representing the relationship between the ideal experimental data and the actual normalized experimental data was computed using equation (2). Thereafter, the overall grey relation grade was calculated by averaging the grey relation coefficient corresponding to the selected response as equation (3).…”
Section: Grey-based Taguchi Analysismentioning
confidence: 99%
“…1 Die is widely used to form hard-to-deform materials under extreme condition including high temperature and high pressure, and the service life of dies usually greatly reduces. 2 In order to improve the service life and reduce the manufacturing cost of the die, Zhou et al employed a new method called bimetalgradient-layer surfacing method of welding ferrous alloys with high strength on casting-steel matrix to fabricate die. 3 Compared to the conventional die, it has many advantages such as short manufacturing cycle, low cost and long service life.…”
In order to adapt to the high temperature and heavy load process environment of large forgings, a novel die with “fist-like” structure was designed. The iron-based welding material (RMD248) as the “bone” layer and the nickel-based superalloy welding material (ERNiCr-3) as the “skin” layer were welded on the matrix by wire arc additive manufacture (WAAM). In this work, the grey based Taguchi methodology was used to optimize welding parameters (welding voltage, welding speed and wire feed speed) considering excellent multi-properties (hardness and ultimate tensile strength of high-temperature tensile test) of the dissimilar joint of RMD248 and ERNiCr-3. Further, analysis of variance was done to ascertain the influence of welding parameters on response parameters. Experimental results showed that welding speed was the most effective input parameter followed by wire feed speed and welding voltage. Finally, optimal result was verified through confirmation experiments. Meanwhile, the effect of welding speed on the microstructure and mechanical properties of joint was studied. The microstructures were characterized by optical microscopy (OM), energy dispersive spectrometer (EDS). The results indicated that the microstructure of RMD248 was consisted of more retained austenite at lower welding speed. For ERNiCr-3, the finer columnar crystal structure at higher welding speed was observed. At lower welding speed, the microhardness of RMD248 was just slightly lower, but that of ERNiCr-3 was significantly higher, and the ultimate tensile strength was higher. Therefore, the specimen at lower welding speed had better comprehensive mechanical properties.
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