Tensile and fatigue properties of Fe-Mn-Al-C alloys

The tensile properties and fatigue behaviour of three solution-treated Fe-29 Mn-9 Al-C (wt%) alloys having various carbon contents leading to different volume fractions of austenite and ferrite phases were investigated. The carbon contents were 1.06%, 0.60% and 0.26%, respectively and the corresponding volume fractions of austenite were 100%, 90% and 45%, respectively. The alloy having 1.06% carbon possessed the best tensile properties but its fatigue behaviour was only comparable to the other two alloys with lower carbon contents. The alloy having 0.60% carbon possessed the lowest yield strength, but its fatigue life was slightly better than other two alloys. The alloy having 0.26% C possessed lowest elongation and medium strength, and its fatigue life was comparable to the other two alloys. Their tensile properties and fatigue behaviour were explained in terms of crack initiation, crack propagation, grain size, constituent arrangement and constituent fraction.     

A preliminary study on optimizing the heat treatment of high strength Al–Cu–Mg–Zn alloys

The design of critical aerospace alloys is primarily built on optimizing strength and ductility, both of which can be enhanced by controlling the alloying element additions as well as heat treatment conditions. The 7075 alloy is one such aerospace alloy. The main objective of this study was to optimize the 7075 strength. Several experimental alloys were prepared and tensile test bars were cast using an ASTM B-108 type permanent metallic mold. The as-cast samples were then solution heat-treated at 470 °C for times up to 48 h. The solution heat-treated bars were also aged in order to improve the alloy strength through precipitation hardening. Line scans for Mg, Cu and Zn were obtained from the various heat-treated alloy samples using an electron probe microanalyzer equipped with Energy Dispersive X-ray (EDX) and Wavelength Dispersive Spectroscopic (WDS) facilities. Peaks corresponding to the Mg, Cu and Zn concentrations in the as-cast samples disappeared after solution treatment, reflecting optimized homogeneity structures. The newly developed versions of the 7075 alloy displayed an ultimate tensile strength (UTS) of ∼1 GPa.     

Microstructure characterization and tensile properties of squeeze-cast AlSiMg alloys

A research program was conducted to study the effects of squeeze pressure (70, 100 and 160 MPa) and heat treatment T6 on the structure, hardness and tensile properties of cast Al6Si0.3Mg alloys. The influence of squeeze pressure on macro- and microstructures of Al6Si0.3Mg alloys has been investigated. Some of castings were solution treated at 540 °C for various times and others were subjected to aging at 170 °C after solution treatment. The results indicated that precipitation occurred within about 30 min for both cast and squeeze cast alloys. The hardness began to increase and maximum values were observed after about 10 h for as-cast alloy. Increasing of squeeze pressure (70–160 MPa) accelerated strength of the alloys from 8 to 4 h, respectively. Squeeze pressures decreased the percentage of porosity and increased the density, also it decreased the grain size of α-Al and modified the Si eutectic. Hardness and tensile properties increased with both heat treatment and increasing of squeeze pressure.     

The effects of the processing variables on the microstructure and tensile properties of naturally aged AA6022 wrought alloys

Abstract

The 6xxx series (Al‐Mg‐Si) alloys have properties of medium to high strength, excellent formability, good corrosion resistance, and weldability. In the present paper, we discuss the tensile properties of T4 heat‐treated AA6022 alloys produced by different fabrication processes, including differences in the homogenization temperature, the hot rolling temperature, the cold rolling reduction ratio, and the solid solution temperature. The analysis was done by differential scanning calorimetry, tensile strength testing, by measuring the electrical resistivity, and optical microscopy. The results indicate that the yield strength and the ultimate tensile strength of naturally aged AA6022 alloys increases with increases in the homogenization treatment temperature, hot rolling temperature, cold rolling ratio and solution treatment temperature.     

Influence of martensite volume fraction and tempering time on tensile properties of partially austenitized in the (α + γ) temperature range and quenched + tempered ferritic ductile iron

In the present study, the effect of martensite volume fraction and tempering time on the tensile properties of ferritic ductile iron with dual matrix structure was investigated. For this purpose, specimens were intercritically annealed (partially austenitized) in the two phase region (α + γ) at various temperatures of 795 and 815° C for 20 min and then quenched into oil held at 100° C to obtain different martensite volume fractions. Some specimens were also conventionally heat treated (austenitized at 900° C and then quenched + tempered) for a comparison reason. The results showed that a structure having proeutectoid ferrite plus martensite has been developed and volume fraction of proeutectoid ferrite and martensite can be controlled to influence the strength and ductility. Specimens quenched from the (α + γ) temperature range exhibited much greater ductility than conventionally heat treated specimens. The tensile strength increased and ductility decreased with increasing martensite content. By increasing the tempering time, the yield and UTS decreased and ductility increased. The specimens tempered for 3 h and having 62% martensite volume fraction (MVF) exhibited the best combination of high strength and ductility. The tensile and proof stress of this material is much higher than pearlitic grades and ductility is lower than ferritic grades. The specimen tempered for 3 h and having ∼ 25% MVF exhibited the best combination of high strength and ductility compared to ferritic grades. However its strength is slightly lower but the ductility is almost three times higher than pearlitic grades.     

Optimization of mechanical property,antibacterial property and corrosion resistance of Ti-Cu alloy for dental implant

Ti-Cu alloys with different Cu contents (3, 5 and 7 wt%) were fabricated and studied as novel antibacterial biomaterials for dental application. The Ti-Cu alloys were annealing treated at different temperatures (740 °C, 830 °C and 910 °C) in order to obtain three typical microstructures, α-Ti + Ti₂Cu, α-Ti + transformed β-Ti, and transformed β-Ti. Mechanical, antibacterial and biocorrosion properties of Ti-Cu alloys with different microstructures were well analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile test, electrochemical test and antibacterial test. The results indicated that the Ti-Cu alloys with microstructure of α-Ti + Ti₂Cu showed the best ductility compared with other Ti-Cu alloys with microstructures of α-Ti + transformed β-Ti and complete transformed β-Ti, and meanwhile, increase of the Cu content significantly contributed to the decreased ductility due to the increasing amount of Ti₂Cu, which brought both solid solution strengthening and precipitation strengthening. Finally, the Ti-5Cu alloy with microstructure of α-Ti + Ti₂Cu exhibited excellent ductility, antibacterial property and corrosion resistance, providing a great potential in clinical application for dental implants.     

Effect of soaking time and concentration of NaOH solution on mechanical properties of coir–polyester composites

The green husk coir fibres were treated with different levels of soaking time and concentration of alkali solution. As a result of alkali treatment, the surface modifications were done on the fibre surface and were studied using scanning electron micrographs. The coir?Cpolyester composites were fabricated using hand lay up process and the mechanical properties (tensile, flexural and impact strength) were evaluated as per ASTM standards. The effect of soaking time and concentration of NaOH solution were studied based on evaluated values of mechanical properties to find out optimum fibre treatment parameters.     

Effect of microstructure and texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloys

This work mainly studied the influence of the microstructure and crystallographic texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloys with different Y contents. The samples were machined from thick plates obtained by extrusion and the tensile tests were performed parallel to extrusion and transverse directions, respectively. Microstructure observation firmly indicated that the grain-refining effect of icosahedral quasicrystal phase (I-phase) was superior to that of the cubic W-phase. In addition, the tensile results indicated that I-phase could effectively improve the strength (yield strength and ultimate tensile strength) of alloys. However, strengthening effect of W-phase was lower. With the quantity of W-phase increasing, the strength of alloys was degraded. It also showed that the alloys were mechanically anisotropic, i.e. the longitudinal strength was higher than that of the transverse direction. However, the ductility of the transverse direction was superior. With the increase of Mg–Zn–Y phases, the anisotropy of the ultimate tensile strength (UTS) between the longitudinal and transverse directions increased remarkably. SEM fracture observations showed that the fractures of the TD samples were characterized by the typical “woody fracture”, with a large amount of cracked Mg–Zn–Y particles (I-phase and W-phase) distributed at the bottom of dimples. With Y content increasing, the average spacing of the zonal distributed Mg–Zn–Y particles on the fracture surface became narrow, which influenced the transverse mechanical properties greatly.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.     

Effect of iron additions on mechanical properties of Co3 Ti alloy

High temperature tensile tests were carried out on L1₂ type Co₃ Ti alloys, both undoped and doped with 1–4 at.-%Fe. There were anomalous increases of the 0·2% yield stress (yield strength) with increasing test temperature from 473 to 1073 K (or 1173 K, depending on the composition). The elongation and ultimate tensile stress (UTS) monotonically decreased with increasing temperature. The fracture surfaces of specimens showed a variety of fracture modes which were dependent on the test temperature and composition. There was a correlation between the ductility and the fracture mode: the more transgranular the fracture mode, the higher the ductility. It was found that Co₃ Ti with 2 at.-%Fe exhibited improved ductility and it exhibited the highest peak value of yield strength and peak temperature. The alloys were also hydrogen charged to investigate their hydrogen embrittlement behaviour. Room temperature tests indicated that the addition of 2 at.-%Fe decreased the hydrogen related embrittlement.

MST/3479     

Influence of Silicon Morphology and Mechanical Properties of Piston Alloys

In this paper, the influence of silicon particle morphology on mechanical properties of two piston alloys has been reported. Alloys having nominal composition Al-12%Si-1%Ni-0.8%Cu-0.6%Mg (LM13) and Al-17%Si-1%Ni-0.8%Cu-0.6%Mg (LM28) were prepared by melting and casting. The morphology of silicon crystals was changed using additives during the melt treatment and subsequently by heat treatment. Mechanical properties such as hardness, ductility, and tensile strength of experimental alloys were tested. Test results showed that the melt treatment and heat treatment of both the alloys increased the tensile strength, hardness, and ductility. However, the influence of melt treatment on mechanical properties was not as significant as that of heat treatment. Tensile strength and ductility of LM13 was found to be higher than the LM28 alloy under similar conditions. Hardness of LM28 was higher than the LM13 alloy. Optical and SEM studies showed a change in eutectic silicon morphology on melt treatment of LM13. However, change in morphology of primary silicon particles was not significant as for LM28. Heat treatment of both alloys caused spheroidization and better distribution of eutectic silicon crystals. Sharp-edged primary silicon particles were rounded off after the heat treatment of LM28. Scanning electron microscopy (SEM) of tensile fractured surfaces was carried out to study the influence of microstructure on fracture mode. Heat treatment of both alloys promotes dimple fracture. However, as-cast and melt-treated alloys show predominantly cleavage fracture.     

Effect of chromium content on electrical resistivity and tensile properties of Ti–Fe–Cr alloys

Abstract

The effects of substituting chromium for iron and the use of low cost ferrochromium alloys in the production of β-Ti–Fe–Cr alloys have been studied with respect to phase constitution, stability, and mechanical properties, in solution treated and quenched states using resistivity, hardness measurement, X-ray diffraction, and tensile testing. Resistivity at room and liquid nitrogen temperatures, and hardness decreased while the ratio of resistivity at liquid nitrogen temperature to that at room temperature increased with increases in chromium content. Alloys of Ti–Fe–Cr, with almost the same electron per atom value, with higher chromium content have smaller volume fractions of athermal omega than alloys with higher iron content. There is less solution hardening in the former alloys than in the latter alloys. Tensile strength decreased with increases in chromium content, while elongation and reduction in area significantly increased. The balance between tensile strength and ductility (elongation and reduction in area) improved in the alloys with added chromium as a substitute for iron. Therefore, no negative influences of ferrochromium alloying on mechanical properties was observed in this study.     

航空紧固件用Ti-5553合金的组织和性能

采用扫描电镜和透射电子显微镜研究不同热处理制度对Ti-5553高强钛合金显微组织与力学性能的影响。结果表明:在(α+β)两相区进行固溶处理时,随着固溶温度的升高,Ti-5553合金组织中的初生α相含量逐渐减少,β相的尺寸和体积分数均增加,合金强度逐渐降低。时效后β基体发生转变,晶界和晶内析出大量次生α相。次生α相的尺寸对力学性能产生重要影响,随着时效温度的升高,次生α相逐渐粗化,导致抗拉强度逐渐下降。1240MPa级航空紧固件用Ti-5553的固溶温度应选择Tβ以下,使组织中留有足够的β相,从而时效时在β相中有大量次生α相析出,获得需要的高强度。同时,保留一定含量的初生α相,以便获得良好的塑韧性。经810~820℃,1.5h,水淬+510℃,10h,空冷热处理后,合金可以获得较好的综合性能,抗拉强度达1500MPa,伸长率达14.8%,断面收缩率为38.6%。固溶和时效态的拉伸断口均存在大量韧窝,材料具有良好的塑韧性。     

Effect of equal-channel angular extrusion on mechanical and wear properties of eutectic Al–12Si alloy

Mechanical and wear properties of severely deformed Al–12Si alloy by equal-channel angular extrusion/pressing (ECAE/P) were investigated. Multi-pass ECAE processing of the as-cast alloy substantially increased both its strength and ductility. The increase in the tensile and yield strength values after six ECAE passes were about 48% and 87%, respectively. The sample after six ECAE passes exhibited 10% elongation before rupture, which was about five times higher than that of the as-cast one. The improvement in both strength and ductility was mainly attributed to the changes of the shape, size and distribution of the eutectic silicon particles along with the breakage and refined of the large α-Al grains during multi-pass ECAE processing. However, the wear test results surprisingly showed that the ECAE process decreased the wear resistance of the alloy, although there was improvement in strength and ductility values. This was mainly attributed to the tribochemical reaction leading to oxidative wear with the abrasive effect in Al–Si alloys during sliding. The oxide layer played a dominant role in determining the wear resistance of the sample in both as-cast and ECAE-processed states, and it masked the effect of strengthening of alloy structure on the wear resistance.     

Static mechanical properties of cast and sinter-annealed cobalt-chromium surgical implants

Porous-surface-layered surgical implants may be produced by sintering at elevated temperatures. An investigation was undertaken to determine the effect of these sintering heat treatments on the tensile properties of the cobalt-chromium casting alloy specified by ASTM F75-76. Specimens which were given a sintering treatment and then rapidly cooled from elevated temperature were found to lack ductility. This was due to the incipient melting of an interdendritic material which was subsequently retained in the grain boundaries as a brittle solid after quenching. Two methods were found which would reduce the amount of this brittle solid: (i) modify the heat treatment to include a slow cooling step to temperatures below that at which incipient melting first occurred; and (ii) reduce the carbon content of the alloy. Reduced-carbon alloys gave the greatest post-sintering ductility, but showed a lower 0.2% yield stress. The techniques of thermal activation analysis were used to investigate the effect of second phases upon the initial low-strain work-hardening rates and the 0.2% yield stress. It was found that the work-hardening rate from the elastic limit to a total strain of about 0.01 to 0.02 depends, in part, directly on the volume fraction of second phase.     

Influence of fluidized sand bed heat treatment on the performance of Al–Si cast alloys

The present study was undertaken to arrive at a better understanding of the effects of solution heat-treatment time and melt treatment on the microstructure and tensile properties of T6-tempered A356.2 and B319.2 cast alloys heat treated using a fluidized sand bed furnace (FB) as opposed to a conventional convection furnace (CF). The alloys investigated were subjected to solution heat treatment at 530 °C and 495 °C, respectively, for times ranging from 0.5 to 24 h, warm water quenching, and conventional T6 aging at 155 °C and 180 °C, respectively, for times of 0.5, 1, 5, 8 and 12 h. The results revealed that the tensile strength of these alloys is more responsive to an FB heat treatment than to a CF treatment for solution treatment times of up to 8 h. A significant increase in strength is observed in the FB heat-treated samples after short aging times of 0.5 h and 1 h, the trend continuing up to 5 h. Analysis of the tensile properties in terms of quality index charts showed that both modified and non-modified 319 and 356 alloys display the same quality, or better, after only 2 h treatment in a fluidized bed compared to 10 h using a CF treatment. The 319 alloys show signs of overaging after 8 h of aging using a CF, whereas with an FB, overaging occurs only after 12 h. The Si particle characteristics of the alloys investigated show that the smallest particle size is obtained after solution heat treatment using a fluidized sand bed, the optimum solution heat-treatment time being 0.5 h for modified alloys, and up to 5 h for non-modified alloys.     

Tensile properties of partially austenitised and austempered ductile irons with dual matrix structures

Abstract

In the present study, an unalloyed ductile iron containing Fe–3·50C–2·63Si–0·318Mn–0.047Mg (wt-%) were intercritically austenitised (partially austenitised) in two phase region α+γ at various temperatures of 795, 805, 815 and 830°C for 20 min and then quenched into salt bath held at austempering temperature of 365°C for various times to obtain different ausferrite volume fractions (AFVFs). Results showed that dual matrix structure containing proeutectoid ferrite, new ferrite (also called epitaxial ferrite) and ausferrite (bainitic ferrite+high carbon austenite, which is retained or stabilised austenite) has been developed. Within each of the austempered series in α+γ temperature range, new ferrite volume fraction increased with increasing intercritical austenitising temperature (ICAT). Although, transforming percentage of new ferrite from parent austenite present at ICAT increased with decreasing ICAT. Some specimens were also conventionally austempered from 900°C for comparison. The new ferrite was absent in these samples. The volume fraction of proeutectoid ferrite, new ferrite and ausferrite can be controlled to determine the strength and ductility. Austempered specimens in α+γ temperature range exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing AFVF. On the other hand, the ductility increased with increasing proeutectoid ferrite and new ferrite volume fractions at the expense of strength. The specimen with ～47·2%AFVF exhibited the best combination of high strength and ductility. The strength and ductility of this material is much higher than that of ferritic grades. Its strength is at the same level as while ductility almost more than four times higher than that of pearlitic grades. Meanwhile, the specimen with ～ 75%AFVF exhibited the best combination of high strength and ductility compared with those of pearlitic grades. The strength of this material is much higher and its ductility is almost more than two times higher than that of pearlitic grades yet slightly lower than that of ferritic grades. This material also meets the requirements for the strength of quenched and tempered grades and its ductility is higher than that of this grade.     

Comparison of mechanical properties for equiaxed fine-grained and dendritic high-palladium alloys

Two Pd-Cu-Ga alloys and a Pd-Ga alloy were selected for study. Bars of each alloy were tested in tension for the as-cast and simulated porcelain-firing conditions, and values of mechanical properties were measured. Fracture surfaces and microstructures of axially sectioned fracture specimens were observed with the SEM. The two Pd-Cu-Ga alloys exhibited similar mechanical properties. The Pd-Ga alloy had lower strength and higher percentage elongation. Heat treatment simulating porcelain firing cycles decreased the strength of both Pd-Cu-Ga alloys and increased their ductility. However, this heat treatment did not significantly affect the mechanical properties of the Pd-Ga alloy. All three high-palladium alloys had the same modulus of elasticity. The amount of overall porosity was relatively minimal (< 1%) and not significantly different among the three alloys. However, porosity was a significant factor for UTS of one Pd-Cu-Ga alloy and the Pd-Ga alloy.     

The effect of martensite volume fraction and particle size on the tensile properties of a surface-carburized AISI 8620 steel with a dual-phase core microstructure

This study is focused on the production of a dual-phase steel structure in the core of a surface-carburized AISI 8620 cementation steel and the effect of martensite volume fraction (MVF) and martensite particle size (MPS) on tensile properties. Experimental results showed that, compared with specimens with a fully martensitic microstructure in the core, those with a dual-phase microstructure in the core exhibited slightly lower tensile and yield strength but superior ductility without sacrificing surface hardness. In specimens with a dual-phase microstructure in the core, the tensile strength increased and ductility decreased with increasing MVF. Both the tensile strength and the ductility increased with decreasing MPS at constant MVF. The best combination of tensile strength and ductility was obtained with a fine MPS at a constant MVF of 25%.     

纺丝液合成因素对木材液化物炭纤维原丝性能的影响

利用木材苯酚液化物合成纺丝液, 熔融纺丝制成新的炭纤维原丝, 研究了纺丝液合成因素对原丝性能的影响。试验结果表明: 增加合成纺丝液时液化原料中的苯酚/木材比(液固比), 则原丝的力学性能提高明显, 其中液固比由3增加至4时, 原丝拉伸强度增加了近9倍; 合成剂用量的增加却导致原丝力学性能的降低, 当合成剂用量为6%时, 原丝的拉伸强度和拉伸模量降幅较明显, 而断裂伸长率的最大降幅却出现在合成剂用量为4%时; 原丝的拉伸强度和拉伸模量随合成温度的升高而增加, 但增幅较小, 断裂伸长率随合成温度的升高却呈下降趋势, 且从110℃升高到115℃时断裂伸长率降幅较大; 原丝的力学性能随合成纺丝液升温时间的增加而先升高后降低, 升温时间为40min时制备的炭纤维原丝的力学性能最优。