HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 bulk powder samples were prepared by citrate route. The phase purity and the structural properties of the samples were examined by x-ray diffraction and Raman spectroscopic measurements. The dc magnetization data revealed that the Cr3+ ordering temperatures (Néel temperature) for the HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 samples are 140 K, 148 K, and 167 K, respectively, while the ac magnetization data revealed that the rare-earth (Ho) ordering occurs at ∼8 K for HoCrO3 and Ho0.67Gd0.33CrO3 samples. Temperature-induced magnetization reversal and spin reorientation were observed in GdCrO3 bulk sample, which depends on applied magnetic field and disappears at ∼1500 Oe and 500 Oe, respectively. By fitting the dc magnetic data with Curie-Weiss law, the effective magnetic moments were calculated to be 11.66 μB, 10.23 μB, and 9.90 μB for the HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 samples, respectively. The isothermal magnetization data showed that the magnetic behavior changed from canted antiferromagnetic in low temperature region (below Néel temperature) to paramagnetic at high temperature. It was found that Gd substitution considerably improves the magnetocaloric effect of HoCrO3. Pure GdCrO3 bulk sample showed giant magnetocaloric entropy change (31.6 J/kg K at temperature ∼5 K and at ∼70 kOe), which is higher than that for polycrystalline RMnO3, RCrO3, and RFeO3 bulk powder samples. This renders GdCrO3 useful for potential applications in low-temperature magnetic refrigeration.
Abstract. It was prepared that Cu 20 Fe 80 alloys using the mechanical alloying and cold pressing and the microwave sintering. The microstructure and the phase composition of Cu 20 Fe 80 alloy were analyzed by SEM and XRD, respectively. The density and hardness of the alloys were measured. The effect of La 2 O 3 on microstructure and properties of Cu 20 Fe 80 alloy was investigated during the microwave sintering. The results have shown that the powder milling structure of Cu 20 Fe 80 alloy is a flake layer which is refined and the mechanical alloying enhanced with increasing La 2 O 3 content; The microstructure of the Cu 20 Fe 80 alloy powder blank cold pressed is lamellar which gradually become dense, the density increases and the formability is improved with the increase of La 2 O 3 content; The microstructure of the Cu 20 Fe 80 alloys sintering was lamellar that the voids and the density and the hardness change with the increase of La 2 O 3 content and the best La 2 O 3 content was 0.2%.
IntroductionIron -Copper -based powder metallurgy bearing material, which can save non-ferrous metals and reduce the cost of raw materials [1][2][3]. But the traditional bearing mixed iron copper powder, the compressive strength, hardness is based on copper based materials on the increased slightly, poor corrosion resistance, and will inevitably generate and microstructure segregation caused by inhomogeneity of hard phase and the performance of the resulting running noise increases and shorten the service life of the bearing, the in the large-scale automation production process, is not conducive to ensure the consistency and stability of the product performance [4][5][6][7] . In this paper, La 2 O 3 was added in the preparation of Cu-Fe alloy, and the effect of La 2 O 3 on the microstructure and properties of Cu-Fe alloy during mechanical alloying and cold pressing microwave sintering was studied.
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