| 1. |
- Feng, Pei Zhong, et al.
(författare)
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Study on Oxidation Behavior of (W, Mo) Si2 Powders in Air at 400, 500 and 600textordmasculineC
- 2007
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Ingår i: Progress in powder metallurgy. - Uetikon-Zürich : Trans Tech Publications Inc.. ; , s. 1289-1292
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Konferensbidrag (refereegranskat)abstract
- The oxidation of (W,Mo)Si2 powders has been examined at 400, 500 and 600°C for 12.0 hours in air. It was shown that the low temperature oxidation resistance of (W,Mo)Si2 was worse than that of MoSi 2, and they showed great changes in mass, volume and colour. At 500°C, the amount of volume expansion of (W,Mo)Si2 was as high as about 7-8 times and color changed from black to yellow after 4.0h with MoO 3, WO3, (W,Mo)O3 and amorphous SiO2 as main reaction products. It took about 8.0h to obtain the same results for MoSi2. The mass gain and oxidation rate were relatively slower at 400°C and 600°C than that at 500°C These were probably due to the lower oxidation rate at 400°C and the protective silica glass on surface of powders formed from the volatilization of MoO3, WO3 and (W,Mo)O3 at 600°C, which would restrain the diffusion of molybdenum from matrix to exterior and oxygen from outside to inside and the further accelerated oxidation.
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| 2. |
- Islam, Syed Humail, et al.
(författare)
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Microstructure and tensile properties of tungsten heavy alloys
- 2007
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Ingår i: Progress in powder metallurgy. - Uetikon-Zürich : Trans Tech Publications Inc.. ; , s. 561-564
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Konferensbidrag (refereegranskat)abstract
- Mechanical properties of tungsten heavy alloys are dependent on many factors including the purity of the raw materials, their tungsten content, manufacturing parameters and the microstructure of the final compact. The main object of this research was to examine the effect of sintering conditions (temperature and time) on the microstructure of tungsten heavy alloys and how the resulting modification of the microstructure can be used to optimize their mechanical properties. Alloys composed of 88%, 93% and 95% wt. of tungsten with the balance of Ni: Fe in the ratio of 7:3 were consolidated into green compacts. Samples of each of the three resulting alloys were sintered at different temperatures (1350°C,1450°C and 1500 0C) for different sintering holding times (3 and 30 minutes) in hydrogen atmosphere. Standard metallographic procedures were used to obtain SEM micrographs. The mechanical properties of tungsten heavy alloys were found to be dependent on the microstructural parameters such as W particle size, solid volume fraction, connectivity and w-w contiguity. It was shown that the mechanical properties of the alloys, and especially their ductility, are harmed when tungsten grains are contiguous.
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| 3. |
- Tian, Jian-jun, et al.
(författare)
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Influence of heat treatment on fracture and magnetic properties of radially oriented Sm 2 Co 17 permanent magnets
- 2007
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Ingår i: Transactions of Nonferrous Metals Society of China. - 1003-6326 .- 2210-3384. ; 17:3, s. 491-495
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Tidskriftsartikel (refereegranskat)abstract
- The quenching, fracture and aging treatment of radially oriented Sm2Co17 ring magnets were investigated. The results indicate that the ring magnets have obvious anisotropy of thermal expansion, which easily leads to the splits of the magnets during quenching. The fracture is brittle cleavage fracture. The difference (δa) of the expansion coefficient reaches the maximum value at 800–850 °C. So, various quenching processes at different steps are adopted in order to reduce the splits. When the magnets are aged. 1:5 phase precipitates from the 2:17 matrix phase and forms a cellular microstructure with 2:17 phase. BHmax and 3Hc reach the maximum value 226 kJ/m3 and 2170 kA/m after being aged at 850 °C for 4 h and 8 h, respectively. The aging treatment at 850 °C has little influence on remanence(Br), which can always keep a high value (≥1.0 T). Through appropriate heat treatment, the ring magnets have uniform cellular microstructure and excellent magnetic properties: Br1.0T, 3Hc≥2 100 kA/m, BHmax≥220 kJ/m3.
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