Effect of corrosion on mechanical behaviors of Mg-Zn-Zr alloy in simulated body fluid

The main purpose of this paper is to investigate the effect of corrosion on mechanical behaviors of the Mg-Zn-Zr alloy immersed in simulated body fluid （SBF） with different immersion times. The corrosion behavior of the materials in SBF was determined by immersion tests. The surfaces of the corroded alloys were examined by SEM. The tensile samples of the extruded Mg-2Zn-0.8Zr magnesium alloy were immersed in the SBF for 0, 4, 7, 10, 14, 21 and 28 d. The tensile mechanical behaviors of test samples were performed on an electronic tensile testing machine. SEM was used to observe the fracture morphology. It was found that with extension of the immersion time, the ultimate tensile strength （UTS）, yield strength （YS） and elongation （EL） of the Mg-2Zn-0.8Zr samples decreased rapidly at first and then decreased slowly. The main fracture mechanism of the alloy transformed from ductile fracture to cleavage fracture with the increasing immersion times, which can be attributed to stress concentration and embrittlement caused by pit corrosion.     

Effect of Trace Elements P and Si(Mn) on Hydrogen Embrittlement of JBK-75 Alloy

High purity hot hydrogn charging at high temperature was used to investigate the hydrogen embrittlement (HE) of JBK-75 alloys with different contents of P and Si(Mn). The results indicated that by lowering P content, the size and distribution γ' precipitate became more homogeneous and the precipitation of stable phase η was retarded, thus the hydrogen resistant properties of the alloy wes obviously improved; however, when Si(Mn) content was lowered together with P, though the size and density of γ' were also homogeneous and no η phase was observed, formation of some micro twin around grain boundaries was found to be detrimental to the hydrogen performance of the alloy. and hydrogen induced loss of area reduction was very high. Therefore, to improve the hydrogen resistant properties of the alloy, P content should be lowered while certain amount of Si(Mn) should be kept     

Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was determined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treatedsteel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested     

Effect of Post-weld Heat Treatment on Properties of Friction Welded Joint Between TC4 Titanium Alloy and 40Cr Steel Rods

Dissimilar metal joining of Ti–6Al–4V(TC4) titanium alloy to as-rolled 40 Cr steel rods was conducted with friction welding, and the effect of post-weld heat treatment(PWHT) on the microstructure and mechanical properties of the resultant joints was investigated. The average tensile strength of the as-welded joints reached 766 MPa and failure occurred in 40 Cr steel base metal. However, after PWHT at 600 °C for 0.5, 1, 2 and 3 h, the tensile strength of the joints decreased and fracture happened through the interface with quasi-cleavage features. The bending angle of specimens was improved from 9.6° in as-welded state to 32.5° after PWHT for 2 h. The tensile strength of the joint was enhanced by martensitic transformation near the interface in as-welded state. Sorbite formed near the interface in PWHT state and improved the bending ductility of the joint. Ti C brittle phase formed at the interface after PWHT for 0.5 h and deteriorated the tensile strength and bending ductility of the joint. After PWHT for 2 h, no Ti C phase was detected at the interface. The microhardness on the interface in as-welded state was higher than that after PWHT, indicating that the decrease of microhardness around the interface could be accompanied by degradation of tensile strength but improvement of bending ductility of the joints.     

Introduction of a New Method for Regulating Laves Phases in Inconel 718 Superalloy during a Laser-Repairing ProcessOA

The morphology, size, and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718) superalloy. Due to the deterioration of the substrate zone, the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment. In this study, an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy ...     

Notch Effect of Materials： Strengthening or Weakening？

Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for structural design and materials selection. In the present work, we tried to find this universal equation from experimental results of metallic glasses （MGs） and other materials as well as theoretical derivations based on a universal fracture criterion （Qu and Zhang, Sci. Rep. 3 （2013） 1117）. Experimental results showed that the notch effect of the studied MG was affected by the notch geometry characterized by the stress concentration factor Kt. As Kt becomes smaller, the notch strength ratio （NSR, which is the ratio of nominal ultimate tensile strength （UTS） of the notched sample to UTS of the unnotched sample） increases. By comparing MGs with other materials like brittle ceramics and ductile for ductile metals but smaller for brittle effect on strength of materials： NSR = equation was found to be consistent with crystalline metals, we find that when Kt is same, the NSR is larger ceramics. Theoretically, we derived a universal equation for notch M/Kt, where M is a constant related to materials. This universal the experimental results.     

A Damage-tolerant Bulk Metallic Glass at Liquid-nitrogen Temperature

Tensile tests and notch toughness tests were conducted on Zr61Ti2Cu25Al12 glass （ZT） at room temperature and liquid-nitrogen temperature. The tensile strength of ZT was improved from 1.63 GPa at room temperature to 1.72 GPa at liquid-nitrogen temperature. Micro-notches with a root radius of 1-3μm were introduced to test the notch toughness of ZT at room temperature and liquid-nitrogen temperature. The test results revealed that the notch toughness of ZT at liquid-nitrogen temperature is comparable to that of ZT at room temperature. The combination of high yield strength and notch toughness of ZT at liquid-nitrogen temperature is comparable to that of the best cryogenic engineering materials.     

Effect of Phosphorus on Stress Rupture Properties of GH4133 Ni—Base Superalloy

The effect of phosphorus on the stress rupture property of GH4133 alloy has been investigated and is compared with that of IN718 alloy. The GH4133 alloy is crept by dislocation movement. Phosphorus has a tendency to prolong the rupture life of some wrought superalloys by inhibiting the dislocation movement. If the phosphorus addition is too high, its effect on impairing the grain boundary cohesion overwhelms that on inhibiting the dislocation movement,and the life of the GH4133 alloy can be shortened. The two functions of inhibiting the dislocation movement and impairing the grain boundary cohesion determine that the optimum phosphorus content in the GH4133 alloy is around 0.011 wt pct. Phosphorus exhibits a greater effect on prolonging the rupture life of IN718 alloy than that of GH4133 alloy. The two alloys are crept by different mechanisms. The intergranular phosphorus-bearing phase is precipitated in the IN718 alloy, while not in the GH4133 alloy. The precipitation of the phosphorus bearing phase can balance the phosphorus segregation at the grain boundaries and allows a more remarkable effect of phosphorus on extending the rupture life of IN718 alloy.     

ω-Assisted refinement of α phase and its effect on the tensile properties of a near β titanium alloy

In this work, the phase transformation sequence during the continuous heating process(3℃/min) was investigated in a near β titanium alloy. The results show that the staring formation of ω phase is about267℃, and the ending precipitation temperature about 386℃ during the heating process. When the heating temperature is greater than 485℃, there are no ω phase detected within the β matrix. Combined with the microstructural characterization, it is found that ω phase facilitates the nucleation of αphase nearby the ω/β interface and has a great effect on the refinement for α phase. As compared with the specimens directly aged, the specimens with ω-assisted refinement of α phase possess high tensile strength, but there is no yield stage detected on their stress-strain curve. Combined with the analyses of the fracture morphology, the specimens with ω-assisted refinement of α phase present a brittle fracture.This is mainly ascribed to its relatively lager width of grain boundaries and the absence of widmanst?ttenα precipitates.     

Effect of Hydrogen on Dezincification Layer-Induced Stress

The effect of hydrogen on the dezincification layer-induced stress and the susceptibility to SCC was investigated.Experimental results showed that the dezincification layer-induced stress increased with increasing hydrogen concen-tration. and 3×10~(-6) hydrogen could increase the susceptibility to SCC of brass in ammonia solution by 10%.     

Influence of Hydrogen on Dislocation Structure in a Duplex Stainless Steel

The dislocation structure of specimens of aduplex stainless steel with precharged hydrogen hasbeen investigated by transmission electronmicroscopy.The result showed the hydrogen acti-vated dislocation source on phase boundaries offerrite/austenite and makes certain dislocations inaustenite grains move.The dislocation appearancesin each phase in specimens uncharged withhydrogen have been given for comparison.     

Hydrogen Treatment of Cast Ti-6Al-4V Alloy

This paper presents the results of an investiga-tion of the effect of hydrogen treatment onmicrostructures and tensile and low cycle fatigueproperties of a Ti-6Al-4V cast alloy.The phasetransformation and the refining mechanism of thecast microstructure during the process of hydrogentreatment were studied.It was found that afterhydrogen treatment,the coarse Widmanstttenstructure of the as-cast Ti alloy was transformedinto a very fine and equiaxed α+β microstructurewithout any GBα phase.The tensile strength andductility and the low cycle fatigue life of thehydrogen treated specimens were significantly im-proved.     

γ″Precipitate in Inconel 718

The γ"precipitate in Inconel 718 Ni-base superalloy has been investigated using TEM. Based on a calculation of diffraction pattern. the orientation relations between precipitates and matrix are given in detail. The influence of solution temperature on growth of γ" precipitates was investigated. and a γ" precipitate free area near δ phase was found. The coarsening behaviour of γ" precipitates during short time aging is discussed     

Influence of alloy element partitioning on strength of primary α phase in Ti-6Al-4V alloy

The partitioning effect of Al(α-phase stabilizer) and V elements(β-phase stabilizer) on strength of the primary α phases in the α/β Ti-6 Al-4 V alloy with the bimodal microstructure was investigated.It was found that partitioning of Al and V elements took place in the Ti-6 Al-4 V alloy during the recrystallization process,leading to the variation of the content of Al and V elements in the primary α phases with changing the volume fraction of the primary α phase.Nanoindentation tests reveal a general trend that the strength of the primary α phases increases with decreasing the volume fraction of the primary α phases,and such trend is independent on the loading direction relative to the c-axis of the α phase.The enhanced strength is attributed to the increase of the content of Al element in the primary α phase,but it is not dominated evidently by the change of the V content.The solid solution strengthening contributed from both the elastic strain introduced by the solute atoms and the variation of the density of states was estimated theoretically.     

Effect of Primary and Eutectic Mg_2Si Crystal Modifications on the Mechanical Properties and Sliding Wear Behaviour of an Al–20Mg_2Si–2Cu–xBi Composite

This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg_2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg_2 Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt%resulted in a loss of modification, possibly due to the formation of Al_8 MgB iS i4 compound before the precipitation of the primary Mg_2 Si. Additionally, the structure of the pseudo-eutectic Mg_2 Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al_5 Fe Si(β), Al_2Cu(θ) and Al_5Cu_2Mg_8Si_6(Q) intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg_2 Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg_2 Si particles.     

Cavitation Erosion Behavior of CrMnN Duplex Stainless Steel in Distilled Water and 3% NaCl Solution

The cavitation erosion (CE) behavior of CrMnN ferrite-austenite duplex stainless steel in distilled water and 3% NaCl solution was investigated by using a magnetostrictive-induced CE facility. The damaged surfaces were observed by scanning electron microscope (SEM). It was found that the CE resistance of CrMnN steel was higher than that of 0Crl3Ni5Mo steel. The mass loss rate of CrMnN steel in distilled water was similar to that in 3% NaCl except at the early stage of CE. The failure mode of ferrite phase was brittle fracture, which had adverse effect on the resistance to CE, while the failure of austenite phase was a ductile failure in CrMnN steel. The excellent resistance to CE was related to the good mechanical properties of austenitic phase and the consumption of CE energy by plastic deformation involving slip and twinning.     

Mechanical Properties and Microstructure of 6082-T6 Aluminum Alloy Joints by Self-support Friction Stir Welding

The majority of this research has concentrated on developing the self-support friction stir welding（SSFSW） tool which consists of a big concave upper shoulder and a small convex lower shoulder, and procedures for making reliable welds in aluminum hollow extrusion. The 5-mm-thick 6082-T6 aluminum alloy was self-support friction stir welded at a constant tool rotation speed of 800 r/min. The effect of welding speed on microstructure and mechanical properties was investigated. The results of transverse tensile test indicated that the tensile strength of joints increased and the elongation decreased with increasing welding speed. The whole values of microhardness of SSFSW joints increased with increasing welding speed from 10 to 200 mm/min. The defectfree joints were obtained at lower welding speeds and the tensile fracture was located at the heat-affected zone（HAZ） adjacent to the thermo-mechanically affected zone（TMAZ） on the advancing side. The investigation of the flow pattern of the softened metal around the SSFSW tool revealed that the flow pattern of the softened metal was driven by two shoulders and the stir pin. The failure of specimens in tension presented the ductile fracture mode.     

Influence of Voids on the Tensile Performance of Carbon/epoxy Fabric Laminates

This paper aims at investigating the effect of voids on the tensile properties of [(±45)4/(0,90)/(±45)2] S and [(±45)/0 4/(±45)(0,90)] S composites.Specimens with void contents in the range of 0.4% to 9.0% were fabricated from carbon/epoxy fabric.The void content was determined by ultrasonic attenuation and optical image analysis,and microscopic inspection was also used to analyze the shape and size of the voids.The influence of voids on the tensile strength and modulus of both stacking sequence is compared in terms of the size and the shape of the voids.The effect of voids on the initiation and propagation of tensile failure of both stacking sequence composite was investigated.     

Process Parameter Optimization of the Pulsed Current Argon Tungsten Arc Welding of Titanium Alloyin process parameter selection of pulsed current gas tungsten arc welding of titanium alloy

The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.     

Cracking Mechanism of Medium-High Carbon Steel during Hardfacing and Effect of Electrode Composition

In this paper,the temperature and stress fields during hardfacing and the crack mor-phology in welded specimens were studied by using a medium-high carbon steel 60CrMnMo, and a RE-doped electrode for cracking resistance has been developed.The temperature fields on the upper surface of simulated specimens during the hardfacing and the following colding were measured by a thermovision analyzer and the residual stress fields were determined by an X-ray stress analyzer. Both these fields have been simulated by usmg the FEM. The calculated re-sults of the temperature and the residual stress fields talhed with the measured ones quite well. The calcu-lations for establishing the influence of martensite transformation temperatures of the hardfacing metal on the stress distribution m simulated specimens show that,with their lowering,the peaks of tensile residual stress at dangerous positions reduce which is considered to be benefit to avoid the occurence of hardfacing cracks.It is shown that,by adding the RE-oxi