Journal of Advanced Materials in Engineering (Esteghlal)

In this paper, the phase formation process of Mn_2.5Ge samples, prepared by mechanical alloying of Mn and Ge metal powders and annealing, has been studied. Results showed that in the milled samples the stable phase is Mn₁₁Ge₈ compound with orthorhombic structure and Pnam space group. The value of saturation magnetization increases by increasing milling time from 0.2 up to 1.95 (Am²Kg^-1). The remanece of the samples increases by increasing the milling time while the coercivity decreases. Annealing of 15-hour milled sample results in disappearance of Mn and Ge and the formation of new phases of Mn₃Ge, Mn₅Ge₂, Mn₅Ge₃ and Mn_2.3Ge. Mn₃Ge is the main phase with Do₂₂ tetragonal structure and I4/mmm space group which is stable and dominant. The enhancement of saturation magnetization in the annealed sample is related to the formation of three new magnetic phases and the increase of coercivity is due to the presence of Mn₃Ge compound with tetragonal structure. Studies were replicated on samples made by arc melting method to compare the results and to investigate the effect of the preparation method on phase formation and structural and magnetic properties of the materials. In these samples the saturation value was in range of 0.2 up to 1.95 (Am²Kg^-1) depending on preparation methods. Rietveld refinement shows that Mn_2.3Ge sample prepared from arc melted under 620^oC anealing is single phase. Magnetic analysis of this sample show a saturation magnetization of 5.252(Am²Kg^-1) and 0.005 T coercive field.

In this paper the effect of deep cryogenic treatment time on microstructure and tribological behavior of AISI 5120 case hardennig steel is studied. The disk shape samples were carburized at 920 ^◦C for 6 hours and air cooled; after austenitizing, the samples were quenched in oil.Then immediately after quenching and sanding, the sample were kept in liquid nitrogen for 1, 24, 30 and 48 h and then tempered at 200 ^◦C for 2 hours. The wear test was done by ball on disk method using of WC ball at 80 and 110 N load. For characterization of carbides, the etchant solution of CuCl₂ (5 gr)+HCl (100 mL) + ethanol (100 mL) was used. The hardness of samples before and after of tempering was measured by vicers method at 300 N load.. The amount of retained austenite was measured by X Ray Diffraction method. For 1DCT and 24DCT samples it was about 8% and 4%; in the other samples, the retained austenite peal was so decreased that it was not visible. The result showed that the hardness increases by deep cryogenic treatment in all speciments. While wear resistance increases in 1DCT and 24DCT samples, it decreases for 30DCT and 48DCT samples in compare with Conventional heat treatment (CHT) sample in both applied loads, such that , 48DCT sample has the least wear resistance. The cause of increament of hardness is due to reduction in amount of retained austenite as a result of deep cryogenic treatment and decreasing in wear resistance after 24 hour, is due to carbide growth and nonhemogenuse distribution in microstructure and then weakening of matrix. So the 24 hour deep cryogenic treatment was the best optimal for AISI 5120 steel.

In this research, investigation of the microstructure and magnetic properties of doped barium hexaferrite with cobalt, chromium and tin with BaCo_xCr_xSn_xFe_12-3xO₁₉ (x=0.3,0.5) formula, was performed using solid state method. Phase and structural investigation by X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy respectively, confirmed the formation of barium hexaferrites single phase without the presence of non-magnetic secondary phase after heat treatment for 5 h at temperature of 1000 °C. Also, according to scanning electron microscopy (SEM) images, morphology of particles was perfectly hexagonal with average particle size 200-250 nm. Based on magnetic parameters measured by Vibrating Sample Magnetometer (VSM), both samples were soft magnetic and the highest saturation magnetization was obtained for the sample with composition of BaCo_0.3Cr_0.3Sn_0.3Fe_11.1O₁₉. The values of saturation magnetization (M_s) and the coercivity (H_c) were 42.21 emu/g and 656 Oe respectively for this compound.

Magnesium-manganese ferrite nanopowders (Mg_xMn_1-xFe₂O₄, x=0.0 up to 1 with step 0.2) were prepared by coprecipitation method. The as-prepared samples were pressed with hydrolic press to form a pellet and were sintered in 900, 1050 and 1250˚C. Scanning Tunneling Microscope (STM) images showed the particle size of powders about 17 nm. The X-ray patterns confirmed the formation of cubic single phase spinel structure in samples sintered at 1250˚C. Substituting Mg²⁺ with Mn²⁺ in these samples, the lattice parameter decreased from 8.49 to 8.35Å and magnetization saturation decreased from 74.7 to 21.2emu/g. Also, coercity (H_C ) increased from 5 to 23Oe and Curie temperature (T_C ) increased from 269 to 392˚C. Samples with x= 0.2, 0.4, 0.6 sintered at 1250 ˚C, because of their magnetic properties, can be recommended for hyperthermia applications and for phase shifters.

In this paper, the possibility of elephant foot phenomenon in sintered alloys with volatile components has been studied. To do this, Cu-28Zn brass samples were sintered at the range of 890-970°C for 20 min. The in situ images from brass samples were taken at various sintering conditions. It is concluded that although liquid is pulled down by gravity, but elephant phenomenon was not appeared in these compacts. Instead, the samples were swelled. Chemical composition change and pores coarsening due to zinc evaporation could be considered as the main cause of swelling in brass compacts.

In the present investigation, Mn-Ni binary nano-oxide was deposited by potentiodynamic method on stainless steel at room temperature and the effect of annealing process (at 200 ^oC for 6 h) on microstructure and electrochemical performance of the synthesized pseudocapacitor was studied. The results showed the significant effect of annealing process on increasing the capacitance and decreasing the charge transfer resistance of the electrode. Field Emission Scanning Electron Miscroscopy (FESEM) images depicted interconnected and random nano-flakes in the oxide film microstructure. Moreover, a partially crystallized structure consisting disorder hexagonal birnessite type phase was formed upon annealing in the deposited oxide film with about 10 %at Ni in composition. Based on the galvanostatic charge-discharge plots, the highest specific capacitance (384 F g^-1) and specific energy (53 Wh kg^-1) were found at specific current of 0.1 A g^-1 for the annealed oxide electrode. Finally, cycle life test results at specific current of 10 A g^-1 showed an excellent cyclability and an increase of about 23% in specific capacitance of synthesized pseudocapacitor after 5000 charge-discharge cycles in 1 M Na₂SO₄.

In this research, the TLP bonding of IN-738LC superalloy was investigated using MBF-20 amorphous foil produced by melt spinning process. The bonding process was carried out at 1035-1080°C for 30-60 min under the vacuum atmosphere. Microstructural investigations showed that the eutectic phases formed in non-isothermal solidified zone (ASZ) are  consised of secondary phase borieds rich in nickel, chromium and nickel silicides. Nickel silicide fine precipitates are formed within γ solid solution via solid state precipitation during cooling. The centerline eutectic phases decreased with increase of the bonding time and decrease of amorphous foil thickness. It was found that isothermal solidification was completed when bonding was done at 1055°C for 30 min. However, the isothermal solidification rate decreased with increasing of the bonding temperature up to 1080°C. Unexpectedly, isothermal solidification rate decreased by increasing the tempretarure to 1080°C. The shear strength increased by completing isothermal solidification stage and eliminating brittle secondary phase particles in the centerline of bonding zone.

In this study, creation of a silicon aluminide coating on IN738LC nickel-based superalloy has been investigated, using co-deposition process. Thermochemical calculations indicated the possibility of obtaining a silicon aluminide with NH₄Cl activated pack powder at 900°C, in order to achieve coating with desirable structures. Two powder mixtures with nominal compositions of 7Si-14Al-(1-3) NH₄Cl-Al₂O₃ (wt. %) and 16Si-4Al-(1-3) NH₄Cl-Al₂O₃ (4 and 0.5 Si/Al ratios, respectively) were used. According to the results, both coatings showed multi-layered structures containing AlNi₂Si as dominant phase. In coating created by pack powder with Si/Al ratio of 0.5, a porous and brittle layer of NiSi was formed on the surface which deteriorated the mechanical properties of coating to some extent. It was found that inward diffusion of Al was dominant at the first stage, while afterward, inward diffusion of Si led to conversion of NiAl phase to AlNi₂Si and, finally, to NiSi phase. Eventually, the sample coated by Si/Al=4, showed superior microstructural characteristics, containing desirable AlNi₂Si phase without undesirable brittle NiSi phase.

The aim of the present research is calculation and determination of the temperature distribution in the oxy-gas source line heating process for application in the steel plates. Analytical method was used to calculate the temperature distribution by solving mathematical equations. The temperature distribution was determined with numerical method using MATLAB software. A computerized numerical control line heating apparatus was used for carrying out the processes. ITI thermograph camera was used to measure the temperature. The effect of torch distance, gas flow and torch speed on the temperature distribution at the upper and lower surfaces of plate were evaluated. The changes of temperature distribution were achieved at torch speeds of 120, 200 and 300 mm/min, gas flow of 10, 9 and 8 lit/min and torch distances of 30, 40 and 50 mm. Calculated and measured maximum temperatures reached to 900, 810 and 720 K, and 885, 785, 690 K, at torch speeds of 120, 200, 300 mm/min, respectively. The calculated and measured maximum temperatures at gas flow of 10, 9, 8 lit/min are attained to be 900, 810 and 750 K, and 885, 795 and 740 K, respectively. Maximum calculated and measured temperatures at torch distance of 30, 40 and 50 mm are accomplished to be 900, 880 and 810 K and 885, 840 and 790 K, respectively.