Iranian Journal of Materials Science and Engineering

 In this study, high-carbon, chromium alloy steel (100Cr6) having the initial spheroidized microstructure was welded using the rotary friction welding method. The effects of process parameters such as friction time and friction force were experimentally investigated. The friction welded joints were produced of two 100Cr6 steel rods. In order to examine the microstructure and mechanical properties of the friction welded 100cr6 steel joints, tensile and hardness tests were conducted. The microstructure of weld zone was examined by optical microscopy. It was found that after cooling, martensitic structure is obtained at the core and periphery of the weld joint. It was found that the tensile strength of friction welded samples is increased with increasing time and force of friction up to a certain level and then decreases again. Hardness measurements show a higher hardness at the centre of the weld joint in comparison with its periphery.

In this paper, the effects of solutioning and various aging heat treatment processes on the microstructure, the hardness and electrochemical properties of a duplex stainless steel (DSS) were studied. The evaluation of the microstructure and phase compositions were carried out by the optical microscopy (OM) and the X-ray diffraction (XRD), respectively. Electrochemical behaviors of specimens were evaluated by both potentiodynamic polarization and electrochemical impedance spectra (EIS) tests at temperatures of 25 and 60 ºC. The obtained results showed that the solutioning heat treatment increased corrosion rates with respect to the blank specimen. The aging process at 490 ºC for 20 hrs increased the volume percent of the carbide phase to the highest value (25.1%) which resulted in an increase of the hardness value to 170 VHN. The specimen which was aged at 540 ºC for 10 hrs with the Cr₇C₃ size of 22.8 µm, exhibited the higher corrosion resistance at both temperatures of 25 and 60 ºC with respect to other aged specimens. In addition, the temperature of 60 ºC promoted the anodic reactions in 3.5 wt% NaCl solution which decreased impedance modulus values significantly. Consequently, the carbide size was more effective parameter than the carbide content in predicting electrochemical behaviors of such alloys. 

The effects of erbium (Er) addition at various weight percentages (0-0.6 wt.% at an interval of 0.2) on the microstructural characteristics, tensile response and wear properties of as-cast Al-7.5Si-0.5Mg alloy were evaluated. The microstructure of samples was examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The obtained results demonstrated that the incorporation of erbium obviously decreased the α-Al grain size and eutectic Si, and altered the Si morphology from plate to semi-globular. Further addition of erbium (> 0.2 wt.%) did not alter the eutectic morphology and size. Moreover, the Al₃Er phase was also observed in the eutectic region after modification. Out of the erbium contents used, 0.2 wt.% erbium showed the best influence on the tensile and wear properties. Compared with those of unmodified specimen, the values of ultimate tensile strength and elongation were enhanced by 31% and 39%, respectively with the introduction of 0.2 wt.% erbium. Additionally, a remarkable enhancement in the wear properties was observed with the addition of 0.2 wt.% erbium.
 

Phenomenological methods are more diagnostic tools than a predictor, so multi-crystalline material approaches based on their microstructures have been proposed during the last years. The purpose of this research is to review methods taking into account the effect of microstructures and texture deformation on predicting the behavior of sheet metals. These methods can be categorized into six general groups: Taylor-type models, crystal plasticity finite element methods, strain gradient methods, methods that consider dislocations, self-consistent methods, methods based on fast Fourier transform. This paper attempts to explain and compare these methods that have been used to forecasting forming limits or stress-strain curves.

The influence of melt superheating treatment on the solidification characteristics and microstructure of Al–20%Mg₂Si in-situ composite has been investigated. The results revealed that melt superheating temperature has a significant effect on solidification parameters and morphology of primary Mg₂Si particles. Solidification parameters acquired using cooling curve thermal analysis method, indicate that both nucleation temperature and nucleation undercooling of primary Mg₂Si particles increase by increasing melt superheating temperature, while recalescence undercooling decrease under the same condition. Also, based on the microstructural evaluations, melt superheating treatment can refine primary Mg₂Si particles and alter their morphology from dendritic shape to more spherical shape and the eutectic microstructure of a-Al + Mg₂Si becomes finer and the distance between eutectic layers becomes smaller.
 

The effect of pouring temperature while preparing Al SiC metal matrix composites, with additional benefits of magnesium and copper through stir casting technique were investigated. The composites were fabricated by mixing 12 wt% of SiC reinforcements, 4 wt% magnesium and 2 wt% copper into 6061 aluminium alloy melt at different pouring temperatures (630 ºC, 670 ºC and 710ºC). The addition of magnesium will enhance the wettability of the SiC particles with Al matrix and subsequently increase its interface bonding strength. The inclusion of copper has considerable improvement in strength and hardness of the composite. The microstructure and mechanical properties (tensile strength and hardness) of the Al MMC are evaluated with the corresponding processing parameter, specifically pouring temperature of the cast composite. The metallurgical characterization utilizing optical and scanning electron microscope were observed for the prepared composites. The coarse microstructure and homogenous distribution of alloying elements along with SiC particles were appeared within dendrite structures of the Al SiC composites. The SiC particles has effectively distributed and produced better bonding strength in composites prepared with 670ºC pouring temperature. Higher tensile strength and maximum hardness have occurred in composite at pouring temperature of 670ºC as compared to other composites. The mechanical properties were lower in composites prepared using lesser pouring temperature (630ºC) and significantly decreased for higher pouring temperature (710ºC) of the composites.
 

In this research, the effect of initial microstructure and solution treatment on rollability and crystallographic texture of a Cu-Mn-Ni-Sn alloy has been investigated. The initial tests indicated that the rolling of the alloy at different temperature conditions is not possible due to formation of second phases. Herein to eliminate the segregated phases, according to DTA analysis, proper temperature for solution treatment was selected as 750°C applied at different periods of time. The obtained results showed that after 15-hour solution treatment, the complete elimination of Sn, Mn, Ni, and Fe-rich phases can be achieved. Also, the peaks of XRD shifted to the higher angles indicating that the alloying elements are dissolved. Meanwhile, the intensity of the texture reduced and the dominant texture changed from Goss and Brass-texture to Copper-texture. Accordingly, the amount of maximum total reduction at the rolling process increased from 16.37 to 109.46 after solution treatment.

It has long been thought-provoking and challenging as well for researchers to design and produce a special low-modulus β titanium alloy such as Ti‐35Nb‐7Zr‐5Ta, representing optimal mechanical properties that is needed to successfully simulate bone tissue. In order to identify the key effects of processing pathways on the development of microstructure, Young’s modulus, and strength, a nominal Ti-35Nb-7Zr-5Ta alloy was made via casting, hot forging, homogenizing, cold rolling and finally annealing. Results from tensile test alongside microscopic and XRD analysis confirm the importance influence of processing method on fully β phase microstructure, low elastic modulus and high strength of the alloy. The specimen with post-deformation annealing at 500 °C demonstrated the Young’s modulus of 49.8 GPa, yield strength of 780 MPa and ultimate tensile strength of 890 MPa, all of which are incredibly close to that of bone, hence suitable for orthopedic implants. At temperature above 500 °C, a sharp fall was observed in the mechanical properties.