Journal of Advanced Processes in Materials Engineering
Year:2013 | Volume:6 | Issue:4 (23)|Papers Count:12

In this work the possibility of synthesis of nano crystalline NiTi intermetallic, directly by mechanical alloying (MA) or by crystallization of amorphous phase formed during MA, were investigated. MA process and subsequent heat treatments were performed for two types of elemental nickel and titanium powders. MA process was performed in a planetary ball mill under an argon atmosphere for 50h. The powders morphology, phase formation and amorphization were investigated by X-Ray diffraction, differential scanning calorimetry and scanning electron microscopy. It is revealed that the shape memory NiTi intermetallic with nanometric size is the only component formed after crystallization of amorphous phase obtained by MA, and there was no any other undesirable component in the specimen structure.

Low oxidation resistance of low carbon steel restricts the applications of these materials at elevated temperature. Due to the high corrosion and oxidation resistance of Al base alloys, in this research low carbon steel substrate was subjected to the weld cladding with using Al-rich overlayer. Microstructural studies by using optical and scanning electron microscopes indicated the formation of needle-like Al-rich intermetallic with nearly uniform distribution in the Al clad overlayer. This clad overlayer increased the surface hardness of substrate. Phase analysis by using XRD accompanied with chemical composition studies by EDS analysis revealed that the clad layer was comprised FeAl intermetallic as the matrix with Fe3Al and FeAl3 needle-like intermetallics distributed in the clad layer. Results of oxidation test of samples at 500oC for 10-100hr showed the Al-rich clad improves oxidation resistance of samples significantly. In addition, Al rich overlayer increases surface hardness of substrate to 270 Vickers which is twice of substrate hardness.

In this paper, the effect of temperature and amount of foming agent (silicon carbide) on properties and microstructure of foam glass from waste cathode ray tube display panel and waste soda-lime glass are investigated. To this end, each of the glasses powder prepared in less than 63 mm and then different amounts of silicon carbide (2, 4, 6 and 8 wt%) was added to them. The powders were compacted under uniaxial press and then sintered at vrious temperatures (750-1050oC) with the same sintering program. Physical and mechanical properties of samples such as density, porosity and bending strength were measured. Also microstructural studies of samples were examined by Scanning Electron Microscopy. The results showed that SiC as a foaming agent can control the pore size and creates microstructure with a narrow distribution of pores..The sample with 4% SiC was changed into foam at 850oC, had the most amount porosity (90%) and bending strength (0.57 MPa) but the size of pores was large and  pore distribution was heterogeneous. In the case of cathode ray tube display panel and 6 wt% SiC that was sintered at 950oC for the same time, the highest prosity was about 55% and bending strength was 12 MPa that had relatively uniform microstructure. These properties have been improved in comparison with those of commercial samples.

In this research, interparticle bond formation in powder metallurgy Cu-10Sn-10Pb alloy from mixed powder was investigated. For this purpose Cu, Sn and Pb powders with particle size less than 100 mm were mixed according to the above weight ratio and the prepared powder was compacted at 550 MPa. The compacted samples were sintered in the range of 750 to 800oC, obtained through thermal analysis, for 60 min in Argon atmosphere. Comparing metallographic results and fracture surfaces, the amount of liquid phase, either transient or persistence, was sududied. More homogeneity, in consequence of rearrangement and diffusion of produced liquid phase, was acheived with increasing sintering temperature. Therefore the interparticle bond strength was comparable with particles strength so that transgranular fracture participates more than intergranular fracture.

The purpose of this paper was to investigate corrosion protection, electrochemical response and surface morphology of cerium oxide conversion coating deposited on Al7075-T6 by a spontaneous dip immersion process after different surface treatments. Coatings were deposited by immersing the alloy panel in an aqueous solution of CeCl3 and glycerin. Corrosion behaviors of coatings were monitored in 3.5 wt% NaCl solution at room temperature. It was found that activation of the panel using alkaline etching and then de-smutted in H2SO4 increased corrosion resistance. Analysis of the surface morphology of the coatings showed that the coatings stored at room temperature in laboratory air for 24 h, exhibited fewer visible cracks and the inhibition efficiency 97.66% was obtained.

Martensitic stainless steels applications increase sharply in these decades. Applications cover a big variety of areas including vapor generators, food industries and any application in which an acceptable corrosion resistance and mechanical properties are the main factor in the material selection. In this study the effect of austenizing temperature, tempering period and tempering temperature on the microstructural and mechanical properties of AISI431 martensitic stainless steel were observed using optical microscopy (OM), X-ray diffraction (XRD), tensile, impact and hardness tests. To do this, double austenizing (primary austenizing at 1030oC, oil quenching, tempering at 200oC followed by secondary austenizing at 970oC, oil quenching and tempering at 650oC) was performed on the samples to gain the highest absorbed impact energy and tensile strength. Results showed that with increasing the austenizing temperature from 970 to 1030oC, the absorbed energy in impact test and the tensile strength did not change appreciably. In double austenizing, the maximum absorbed energy in impact test and the highest value in the tensile strength and hardness were achieved as a consequence of dissolving the carbide in the austenite matrix during the primary austenizing treatment. Tempering at low temperatures (200oC) leads to the carbide precipitation in the final structure. Lowering the temperature of second austenizing process prohibited the austenite grains growth and subsequently a small grain sized structure produced. These consequences of heat treatments produce an optimum mechanical property which consists of maximum tensile strength and absorbed energy during the impact test. Furthermore, secondary hardening was observed in AISI431 martensitic stainless steel between 350 to 420oC.

The ever increasing demand for the low loss, low constant dielectrics (for high speed signal transmission) in microwave industry constantly accelerates the search for new microwave dielectrics. Also glass-ceramics have been shown dielectric properties, generally superior to metals and organic polymers. In this report, sintrability and microwave dielectric properties of CaO-SiO2-MgO glass ceramics has been investigated. The results of sinterability demonstrated that this composition is sutable for LTCC technology with low sintering temperature (<1000 oC) 800-860 oC. The glass ceramic prepared at 860 oC exhibited dielectric constant of 6.13 and dielectric loss of 0.0037 in 8-12 GHz.

In the present study the spinning process of clad sheets composed of Copper-Stainless steel 304L investigated experimentally. To produce the Copper-Steel 304L clad sheet the explosive welding method has been used. In order to smooth the surface of clad sheets, a cold roll forming process was done on the sheets. For investigation of diffusion process in interface where copper and stainless steel connected together, to produce a suitable metallurgical bounding and increase formability, the bonded sheets heat treated in duration of 32 hours in 300o C temperature. The mechanical properties of copper-steel clad sheet were extracted by experimental measurements. Then, these welded specimens were put under the EDS and SEM tests to investigate the probability of material diffusion in interface welded. The copper-steel 304L clad sheet with an internal layer of copper and an external layer of steel, used in the spinning process. The effects of influential parameters on the mentioned process including formability, tool path and tool materials on formability of the clad sheets have been investigated. Sub structural investigations on the common surface of metal connection revealed that the cross section of this area is wave-like shape and also heat treatment process increases the formability of clad sheets and causes diffusion of materials remarkably. Final results show that SPK2436 is suitable tool material, the involute curve is the best tool path and the spinning ratio lower than 2.5 is possible to form the clad sheets.

In this paper Al-CNT powder mixtures with 2 and 5% CNT weight percent were synthesized by mechanical alloying. Particle size distribution was measured by laser particle size analyzer. Effect of milling time and carbon nanotube content was characterized on particle size. X-ray diffraction analysis was conducted for different samples and powder crystalline size was measured.  A model was applied for evaluating powder particles strain and stress during mechanical alloying. Powder particles work hardening was calculated by stress-strain curve. In addition a model was used for calculating ball mill efficiency. Powder particle size analyzes showed that by increasing milling time and CNT content a decreased powder particle was obtained. The results of strain and stress curves showed that by increasing milling time and CNT content powder strain and stress increased. Work hardening results showed that increasing milling time result in decreased work hardening. The results showed that the maximum mill efficiency reached to 70% for Al-CNT (%5) and by increasing milling time the efficiency of mill increased. XRD results showed that by increasing milling time and CNT content, decreased crystalline size was obtained.

Formation of Titania thin layer applied on steel substrate was prepared by dip coating method. Titanium Tetra Iso Propoxide (TTIP) was used as precursor. X-ray difraction (XRD) results showed that TiO2 crystallized in the anatase form. Formation of nano scale layer on the substrates was confirmed by scanning electron microscope (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The roughness of thin layer was affected by value of PEG, calcination temperature, number of dipping and pH of sol. In the samples without PEG, increase in number of dipping was led to decrease in roughness, however; different behavior was observed in the samples containing PEG. By increasing the pH value, the coating roughness was decreased.

Mold powders play an important role in process of steel continuous casting such as slab formation. The main tasks are oxidation protection, surface finish, heat loss control, fluidity between mold and solid surface. As an aim of this study some parts of fluorine, due to being poisonous, are replaced by TiO2 and MnO Portland cement clinker, free from sulfates is used, as main Constituent. Groove viscometer, XRD, SEM and EDX are used. Results indicated that by replacing CaF2 with TiO2 and MnO, similar fluidity to that of original powder can be obtained.

In this research work, PTFE/nano-Al2O3 polymer matrix composite powder was prepared by using a high energy ball milling technique under ambient temperature. The morphology, crystalline and molecular structure of the obtained nanocomposite particles were characterized by means of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and Fourier transform infrared spectrophotometer (FTIR) analysis. The results indicated that after ball milling for 20 h, Al2O3 nanoparticles were well deagglomerated and dispersed homogeneously into PTFE particles. It was also shown that milling has no significant effect in deterioration of PTFE crystallites. However, it led to small decrease in the crystallite domains of PTFE. FTIR results showed that there was no obvious chemical modification observed on the PTFE molecular structure after milling.