Sharif Digital Repository

This paper presents the effect of martensite volume fraction (VM) on mechanical properties of AISI 4340 steel with ferrite-bainite-martensite microstructures. The steel bars were austenitized at 900°C for 1h followed by intercritical annealing at 740°C for 100min and quenching into a salt bath with temperature of 300°C and holding at different times to obtain triple phase (TP) microstructures with 34vol.% fraction ferrite and various martensite (or bainite) contents. Presence of three phases in adjacent to each other was confirmed by metallographic analysis and TEM studies. TEM observation also indicates higher density of dislocations within ferrite near martensite colonies compared to that... 

MADI is new engineering material with very desirable properties such as higher strength at the same hardness compared to regular ductile iron, significantly better fatigue performance than regular ductile iron or austempered ductile iron, better machinability than regular austempered ductile iron and similar to as cast ductile iron. In this study,fatigue properties of Machinable Austempering Ductile was investigated using rotary -bend fatigue testing device. Chemical composition of sample was selected on the base of previous work which results in good mechanical properties and low hardness after austempering process. The results of this study,indicates that for an austempered ductile iron... 

This work was carried out to investigate the effect of different Ti concentrations as a modifying agent on the microstructure and tensile properties of an in-situ Al-15 pctMg2Si composite. Cast, modified, homogenized small ingots were extruded at 753 K (480°C) at the extrusion ratio of 18:1 and ram speed of 1 mm/s. Various techniques including metallography, tensile testing, scanning electron microscopy were used to characterize the mechanical behavior, microstructural observations, fracture mechanisms of this composite. The results showed that 0.5 pctTi addition and homogenizing treatment were highly effective in modifying Mg2Si particles. The results also exhibited that the addition of Ti... 

Low-carbon steel sheets are severely plastic deformed to strains of up to ≈3.48 and subsequently heat treated by conventional annealing followed by water-quenching. Four temperatures are chosen for the annealing below and over the Ac1 and Ac3 transformation lines. The effects of post-deformation heat treatment are investigated by evaluating the microstructure and mechanical properties, including strength, ductility, work hardening capability, and hardness. A maximum increase of 86% in the strength is obtained through intercritical annealing and quenching of the samples subjected to strain of 1.16. It is interesting that both the elongation and ultimate tensile strength values are higher... 

AISI 4340 steel bars were heated at 900 °C for one hour, annealed at 738 °C for different durations and oil-quenched in order to obtain dual phase steels with different ferrite volume fractions. A 3% prestrain at the temperature range of 150-450 °C was then imposed to the samples, and room temperature tensile tests were carried out, afterwards. Results indicate that the maximum values for both yield and ultimate tensile strength would exist for the samples pre-strained at the temperature range of 250-300 °C. Also, a sudden drop of the ductility was observed at the mentioned temperature range. The observed behavior might be attributed to the occurrence of dynamic strain aging taken place at... 

A high-quality butt joint of aluminum to copper (Al/Cu) can rarely be achieved by conventional fusion and solid-state welding processes. In this research, the appropriateness of friction stir welding (FSW) for making high-quality Al/Cu welds was studied. A sound Al/Cu butt joint was achieved with relatively high strength in uni-axial tensile tests. Mechanical properties and microstructure of the sound friction stir welds were examined. The ultimate tensile strength of the joints reached about 75 percent of the aluminum base metal, with the fracture occurring at aluminum side. The metallurgical study of the welds before and after their failure in tensile tests showed that the heat affected... 

In this work, examinations on the microstructure and mechanical properties of plain carbon steel and AISI 430 ferritic stainless steel dissimilar welds are carried out. Welding is conducted in both autogenous and using ER309L austenitic filler rod conditions through gas tungsten arc welding process. The results indicate that fully-ferritic and duplex ferritic-martensitic microstructures are formed for autogenous and filler-added welds, respectively. Carbide precipitation and formation of martensite at ferrite grain boundaries (intergranular martensite) as well as grain growth occur in the heat affected zone (HAZ) of AISI 430 steel. It is found that weld heat input can strongly affect grain... 

In-situ aluminum matrix composites were fabricated by 1-3 passes of friction stir process (FSP) using iron (Fe) particles with initial size of 10. μm. Although the initial reinforcing particles were relatively large in size and also agglomerated particles were formed in the obtained composites, all of the processed specimens fractured from the base metal during transverse tensile test. Longitudinal tensile tests revealed that the ultimate tensile strength (UTS) of the composites was up to 43% higher than that of the base metal; however, the strain to fracture of the composites reached to about 0.2. Al-Fe intermetallic compounds (IMCs) formed at the interface of the aluminum matrix and Fe... 

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn-Ag-Cu/CeO 2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO 2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and... 

Aluminium matrix composites reinforced with submicrometre and nanosize Al 2O 3 particles were successfully manufactured in the form of sheets through eight cycles of accumulative roll bonding process. The mechanical properties of the produced composite are compared with accumulative roll bonded commercially pure aluminium. It is shown that only 1 vol.-% of submicrometre or nanosize alumina particles as reinforcement in the structure can significantly improve the yield and ultimate tensile strengths. Scanning electron microscopy revealed that particles have a random and uniform distribution in the matrix especially in the less volume fraction of alumina particles, and strong mechanical... 

In this work, the effect of hot deformation temperature on microstructure and mechanical properties of micro alloyed steel was studied. The results indicated that by decreasing the deformation temperature final microstructure is refined and the volume fraction of grain boundary ferrite is increased and some pearlite is produced. Therefore both the yield strength and ultimate tensile strength is increased, while the toughness is preserved in comparison to a ferritic-pearlitic microstructure. Also a model was developed to relate the deformation condition to the volume fraction of acicular ferrite at mixed microstructure. © 2008 Elsevier Ltd. All rights reserved  

This paper presents the creep behavior of various FRP (GFRP, CFRP, and hybrid) bars in order to investigate the effects of different parameters, including the applied stress levels, bar diameter, and the type of fiber and resin in the creep behavior of FRP bars. The creep strains versus time curves were experimentally obtained for 83 days. Moreover, a statistical study, including analysis of variance (ANOVA) and linear Bayesian regression was conducted to investigate the contribution of the studied parameters. The results showed that in GFRP bars the ratio of ultimate creep strain to the initial elastic strain decreased when the applied stresses on the bars exceeded 30% of their ultimate... 

The grain size of constrained groove pressed aluminum has been predicted through the genetic programming approach. “Sheet thickness,” “elongation,” “yield strength,” “ultimate tensile strength,” “total strain,” and “hardness,” along with “primary grain size” of the ultrafine-grained sheets were utilized as input parameters to obtain the ultimate grain size. A total number of 73 available data in the literature were gathered and randomly divided into 60 and 13 sets for algorithm training and testing, respectively. Among the presented models, the one with best performance utilized parameters of total strain, ultimate tensile strength, and primary grain size with 40 chromosomes, 10 head sizes,... 

In this study, Porous NiTi shape memory alloy has been produced by mechanical alloying of the elemental Ni and Ti powders. The compacting process was done at two temperatures (warm and cold press) and then sintering at 980 and 1050°C was performed on the specimens. Microstructure and mechanical prop-erties of the samples were investigated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. Moreover, shear punch test (SPT) employed to investigate the effect of compaction pressure and sintering temperature on the mechanical properties of the fabricated samples. It was revealed that warm compaction/sintering resulted in 15% yield stress improvement and 20% ultimate... 

Surfaces of cast 1100 aluminum were treated by multi-pass friction stir processing (MP-FSP), which is a solid-state microstructural modification technique using frictional heat and stirring action. An improvement in the mechanical properties was accomplished due to the microstructural modification and reduction of porosities. The yield strengths of the MP-FSPed specimens were significantly increased to about 1.4 times versus that of the base metal. The elongation of MP-FSP sample is about 30% higher than that of the base metal. Also the ultimate tensile strength and hardness of MP-FSPed specimens are improved. Moreover the effect of tool rotation rate and tool travel speed on the mechanical... 

Effects of Fe particle volume percent (from 0 to 5%) and changing the tool rotation direction in each pass were studied on the microstructure evolution and mechanical properties of the in situ Al/intermetallic composites produced by three passes friction stir processing (FSP) with ∼10 µm Fe particles. Optical and scanning electron microscopes were used for the investigation of the composite homogeneity, formation of Al–Fe intermetallic compounds, and fracture surfaces. Tensile and microhardness tests were also carried out to evaluate the mechanical properties of the composites. Solid-state reactions between the aluminum matrix and Fe particles led to in situ formation of Al3Fe and Al5Fe2... 

Dual-phase (DP) steels with different martensite contents were produced by subjecting a low carbon steel to various heat treatment cycles. In order to investigate the effect of dynamic strain aging (DSA) on mechanical properties, tensile specimens were deformed 3% at 300 °C. Room temperature tensile tests of specimens which deformed at 300 °C showed that both yield and ultimate tensile strengths increased, while total elongation decreased. The fatigue limit increased after pre-strain in the DSA temperature range. The effects of martensite volume fraction on mechanical properties were discussed  

Dual phase (DP) steels with network and fibrous martensite were produced by intercritical annealing heat treatment cycles. Some of these steels were deformed at dynamic strain aging temperatures. Room temperature tensile tests of specimens deformed at 300 °C showed that both yield and ultimate tensile strengths for both morphologies increased, while total elongation decreased. Fatigue test results before and after high temperature deformation showed that dynamic strain aging has a stronger effect on fatigue properties of dual phase steels with fibrous martensite. Cracks in DP steels with fibrous martensite propagate in a tortuous path in soft ferrite phase, while they pass of both hard and... 

The unique properties of NiTi alloy, such as its shape memory effect, super-elasticity and biocompatibility, make it ideal material for various applications such as aerospace, micro-electronics and medical device. In order to meet the requirement of increasing applications, great attention has been given to joining of this material to itself and to other materials during past few years. Laser welding has been known as a suitable joining technique for NiTi shape memory alloy. Hence, in this work, a comparative study on laser welding of NiTi wire to itself and to AISI 304 austenitic stainless steel wire has been made. Microstructures, mechanical properties and fracture morphologies of the...