METALLURGICAL ENGINEERING
Year:2018 | Volume:21 | Issue:2 (70)|Papers Count:8

Ni-Cu (70. 4-29. 6; wt%) alloy was prepared by a Vacuum Arc Remelting (VAR) furnace and the effect of thermal treatment on structure and Curie temperature was investigated. The results of Inductively Coupled Plasma(ICP) and EDS analysis showed that specimens with 4 times remeltingwere homogenized. The Curie temperature of alloy that measured by vibrating sample magnetometry (VSM)under condition of slow cooling across from order-disorder transition of alloy was higher than specimens quenched from recrystallization temperature. Curietemperature (TC) of alloy that quenched after melting was 60 oC, TC of sample that annealed in 1000 oC for 24 hours then quenched in water was 40 oC and sample that after annealing twice heated up to 70 oC was 45. 5° C. The d-spacing of the specimen without heat treatment, calculated byX-Ray Diffraction, had a little increase due to clustering. In addition, the surface morphology by optical microscope confirmed this behavior of Cu– Ni alloys in the different heat treatment.

ZrN thin films were deposited on silicon (111) and 304 stainless steel substrates using direct current (DC) reactive magnetron sputtering. The effects of the substrate bias voltage on the films’ structure, morphology, hardness were investigated. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and microhardness tester. XRD patterns showed grain size refinement from 19 to 13 nm with an increase of bias voltage from 0 V to 150 V. In addition, (111) and (200) diffraction peaks were only present and other orientations were omitted. FESEM cross section of ZrN thin films showed a well aligned columnar structure. The increase of bias voltage resulted in hardness rise to about 1720 Vickers at bias voltage of 100 V. Negative bias voltage induce an increase of the films density by the elimination of the porosity and voids. This maximum hardness can be interpreted by a maximum of the film density and minimum of the porosity

Viscosity measurement could provide valuable information for melting and solidification base processes. In this paper a falling ball viscometer is used for measuring molten zinc viscosity. The molten metals are not transparent, some changes are done in the structure of conventional method for tracing ball movement. To solve this problem and in order to trace the movement of the ball (as a falling object) in the melt, a thin steel rod was connected to the ball. The displacement of the ball could then be evaluated from the rod end, which is outside the melt. Viscosity changes versus temperature is studied and as expected the viscosity of the liquid tends to decrease by increasingthe temperature. In the beginning the rate of viscosity reduction was high (0. 004 cP/° C) but then with increasing temperature the rate of viscosity reduction was decreased (0. 0001 cP/° C). Molten zinc is a shear thinning fluid which means by increasing shear rate and mean speed of falling ball the viscosity of molten zinc would drop.

In this research effect of pouring temperature on the microstructure characteristics and hot tensileproperties of an experimental Ni-Fe based superalloy N-155 has been investigated. the melt wasmade in induction furnace by vacuum melting. All samples were poured in the preheated ceramic mould in different pouring temprature include of 1420, 1460, 1500, 1540 and 1580 ° C and cooled down to room temprature in isolated condition. The microstructure charactristics was analised by SEM and EDS techniques. The hot mechanicalproperties was caried out in 816° C for each casting condition. The results show that the main microstructure consist of austenite as only dominate phase and the second perciptation phase concist of MCN carbunitride as shown in continuous films precipteted in a long of grain boundaries. A fine equiaxed / cellural structure can be shown in pouring temprature less than 1460° C due to initial dissolved carbides. The microstructure was modified to coarse dendritic structure enlongated in heat transfer direction at higher pouring temprature around of 1500 ° C. The carbides morphology change from particle-like and coarse film in low pouring temperature to the thin and continous films which precipitated around of grains boundaries. The hot UTS strength reached to 310 Mpa in 1500 ° C due to modified structure and reduced to 245 Mpa because of enlarged grainsand also elongation increases as pouring temperature rises.

Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. Among these, accumulative roll bonding and simple shear extrusion have been extensively used in modern industry. In severe plastic deformations, applied strains have higher values than usual forming methods. Accumulative roll-bonding (ARB) and simple shear extrusion (SSE) processes are two severe plastic deformation processes capable of developing nanostructures. In this research, pure commercial copper was processed with ARB and SSE processes to obtain nanostructure and improve its structure, strength and hardness. Five passes of extrusion and seven passes of rolling were applied on the specimens with the same conditions. After preparing the specimens using both methods, mechanical and structural analyses were performed to evaluate the properties. Mechanical properties were measured using standard tensile and hardness tests. The results show that hardness, yield strength and ultimate tensile strength of the extruded and rolled specimens are increased by increasing the number of cycles. It was concluded that mechanical and structural properties of the specimens produced under ARB conditions appear to be better than SSE process. The layers structures were also studied by optical microscopy.

In this study, microbiologically influenced corrosion because of metabolite sulfate reducing bacteria (SRB) has been investigated in terms of its electrochemical behavior and surface phenomena. According to the results of electrochemical impedance spectroscopy, SRB through changing the bacteria culture medium during the first hour that sample was contacted to the bacteria solution, leads to an increase in corrosion resistance of HSLA-X70 steels from 235 to 1651Ω . cm2. Microstructural examinations on the sample surface embedded in culture medium without bacteria, in comparison to the sample exposed to the culture medium with bacteria, indicate that corrosion products disperse widely which is consistent with the electrochemical tests results. On the contrary, sample exposed to the SRB included bacterial colonies, although shows a reduction in the uniform corrosion rate via the alkalization of the culture medium, provides sites under colonies which are prone to the pitting corrosion. The results of the cyclic polarization test confirm the susceptibility to pitting corrosion of the sample in the bacteria containing solution.

Damage caused by the two-phase gas-solid flow on the immersion tubes into the cyclone in cement industry that involved the environmental corrosive and abrasive factors is very important. In this work, the effect of particle flow and impact on the corrosion of the immersion tube was studied by the simulation of two-phase gas-solid into the cyclone. The results of gas-solid particle flow simulation and investigation on the particle abrasion on the immersion tube were shown that the impact of particle and shear stress is more in the upper half compared to the lower half. In addition, microstructural studies conducted by optical and scanning electron microscopies on the severely corroded sections of immersion tubes were shown that chromium carbide in the grain boundaries of austenite is formed and the cracks nucleated and growth along the grain boundaries of austenite. Formation of chromium carbide in the grain boundaries of austenite caused to decreasing the chromium from the areas adjacent to the grain boundaries, and as a result, intergranular corrosion occurred. Furthermore, the abrasion of the particle impact on the upper half of the immersion tube leading to severe corrosion based on the erosion corrosion mechanism.

In this paper, the effects of pearlitizing on the as cast and as heat-treated microstructures of austenitic manganese steel (named Hadfield steel) were evaluated. The samples with different contents of carbon and manganese were produced using induction furnace and precision casting method. The as-cast, annealed, and solution treated microstructural studies were performed by optical microscopy, X-ray diffraction, ferritescopy and field emission scanning electron microscopy. The microstructural results showed that the as cast and annealed microstructures of the steel in temperature consist of austenite matrix, carbide and ferrite. Fine examination by scanning electron microscope shows that the ferrite and carbide phases are formed as pearlitic colonies. It was also observed that the increase in carbon content and annealing heat treatment are more facilitated the pearlitizing. By applying the final heat treatment (solution and quenching in water), pearlite colonies convert to new fine austenite grains and then the austenite grains sizes are decreased.