Effect of Laser Oscillation on the Microstructure and Mechanical Properties of Laser Melting Deposition Titanium AlloysEI北大核心CSCD

针对激光熔化沉积冶金组织与缺陷,借鉴激光摆动焊接技术,提出一种激光摆动送粉增材制造TC4钛合金工艺,借助激光原位摆动改变熔池运动轨迹进而影响温度梯度和凝固速率,改善增材制造钛合金的微观组织。利用OM、SEM、EBSD和Vickers硬度计研究了激光摆动送粉增材制造工艺对TC4钛合金微观组织演变及力学性能的影响。结果表明,无摆动激光熔化沉积实验的最佳工艺参数为:激光功率1000 W,扫描速率8 mm/s,送粉速率6.92 g/min;直线型激光摆动的最佳工艺参数为:摆动频率200 Hz,摆动幅度1.5 mm。直线型激光摆动对熔池形貌改善显著,气孔和裂纹等缺陷较少,柱状晶数量和尺寸均有所减小,并且晶粒出现了等轴化的现象。相比无摆动样品,激光摆动后Ti-6Al-4V合金单道区域平均晶粒尺寸从5.20μm减小到4.37μm;硬度从418.00 HV提升到428.75 HV。     

Effects of Tempering Temperature on Microstructure and Mechanical Properties of Drill Pipe Steel 26CrMoEI北大核心CSCD

The effects of tempering temperature on microstructure and mechanical properties of steel 26CrMo were studied based on mechanical property tests and microstructure observation. The results show that a phase matrix gradually occurs recovery and recrystallization with increasing temperature during 540 similar to 690 degrees C temper process, martensite morphology fades away gradually, flake or rocklike carbides separate out along the martensite boundaries, and then change into granulated dispersed distribution, at 690 degrees C tempering carbides happen aggregation and growth on grain boundaries. With tempering temperature increasing, the strength of 26CrMo steel is gradually reducing, plasticity and toughness are gradually increasing. The tensile property and impact energy can meet all different grade drill pipe requirements in API 5DP standard with different tempering conditions. The total impact energy, crack initiation energy and crack propagation energy of 26CrMo steel are gradually increasing with the tempering temperature rising, the crack propagation energy is three times of crack initiation energy which shows great anti-crack propagation capability, but their ratio has no obvious change. The change of impact property is closely related to the strength and plasticity change, impact toughness stand or fall depends on high or low plasticity.     

Effect of High-Energy and Instantaneous Electropulsing Treatment on Microstructure and Properties of 42CrMo SteelEI北大核心CSCD

42CrMo steel was widely used in many industry fields for its excellent hardenability and high temperature strength. Many transmission mechanisms and fasteners, such as roller and heat-resistant gear, are made of this steel. However, the ductility of 42CrMo steel is relatively low after quenching and tempering. During high tempering Mo riched carbides at grain boundary and undecomposable martensite at low tempering are the main reasons for poor ductility of 42CrMo steel. Grain refinement can enhance both strength and ductility significantly, but traditional refinement technology will cause intergranular oxidation so that strengthening effect was weak. Although thermomechanical treatment can achieve dynamic recrystallization, its refinement effect is unstable. Elecropulsing treatment, which makes significant change in microstructure and properties of metals, has been applied in many fields such as, modification of solidified microstructure of liquid metal, healing of fatigue crack, nanocrystallization of amorphous materials and so on. Moreover, this process can produce superior mechanical properties in metals. In order to improve the mechanical properties of 42CrMo steel better, high-energy and instantaneous electropulsing treatment was applied. In this contribution, 42CrMo steel was subjected to traditional and electropulsing treatment individually. It was found that EPQ treatment (480 ms electropulsing treatment, water cooled) results in finer grain, promoting the formation of retained austenite and twin martensite; EPT treatment (180 ms electropulsing treatment, air cooled) can stabilize retained austenite in EPQ specimen and induce multiphase structure. Mechanical properties results indicate that strength-ductility balance of EPQ and EPQ+EPT specimen are 32% and 13.9% higher than that of TQ (traditional quenched) and EPQ+TT (traditional tempered) specimen respectively.     

Effect of Fe on Microstructure and Coercivity of SmCo-Based MagnetsEI北大核心CSCD

High-temperature permanent magnets have an important application in the aerospace and other high-tech fields, among which 2:17-type SmCo magnets have become the first choice for high-temperature permanent magnets due to the strong magnetic anisotropy and high Curie temperature. Although there are studies on the effect of Fe on the remanence and coercivity, the role that Fe plays on coercivity mechanism of SmCo magnets is still unclear. In this work, Sm(CobalFexCu0.08-0.10Zr0.03-0.033) z (x= 0.10-0.16, z=6.90 and 7.40) magnets are prepared and the magnetic properties under different temperatures are investigated. The magnets with an intrinsic coercivity of 603.99 kA/m and a maximum energy product of 87.30 kJ/m(3) at 500 degrees C. are obtained. It is revealed that at room temperature the coercivity of the magnets increases with increasing Fe content, however, at 500 degrees C. the coercivity shows an opposite dependency on Fe content. Moreover, the effect of Fe on coercivity is more obvious at low z value. The phase structure and composition analyses were characterized by XRD and TEM. The results show that with the increase of Fe content, the size of the 2: 17R cell phase increases, the volume ratio of cell boundary 1: 5H phase decreases, and furthermore, both Fe content in the 2: 17R phase and Cu content in the 1: 5H phase increase. The variations of Fe and Cu contents in both phases lead to the change of the domain wall energy difference. With the increase of Cu content of 1:5H phase, the domain wall energy of 1: 5H phase (gamma(1:6)) drops faster at room temperature, the coercivity is determined by gamma(2:17)-gamma(1:5), so the coercivity increases with increasing Fe content. While at 500 degrees C, due to gamma(1:6) at its Curie temperature, the coercivity is mainly determined by the domain wall energy of 2: 17R phase (gamma(1:17)), which decreases with increasing Fe content. The increase of Fe content at the low z value results in a smaller growth of cell size, which leads to a more significant change in coercivity.     

Effect of Partial Recrystallization on Microstructure and Mechanical Properties for Cross-rolled Molybdenum Sheet

The paper presented here reports an appropriate static heat tretment and analyses the microstructure with different partially recrystallized annealing temperatures of cross-rolled molybdenum sheet in order to improve mechanical property of this type of materials and reduce anisotropy at the same time for perspective application. Five different temperature ranges are chosen in this experiment. The samples of a cross-rolled molybdenum sheet are obtained through powder metallurgy, forged ingots and hot or cold rolled sheet. A period of first-stage annealing at 800℃ for one hour is not qualified for the further processing because of bad plasticity, working hardening and crack on the surface. The appropriate second-stage annealing temperature at 950℃ for one hour is chosen for improving the elongation and reduces yield strength. The results show that this appropriate partially recrystallized annealing treatment has achieved the ideal grain size and mechanical properties when it is compared with the other four different temperatures with the same second-stage annealing conditions.     

Effect of Ag on the Microstructure,Mechanical and Bio-corrosion Properties of Fe–30Mn Alloy

In the current work, biodegradable Fe–30 Mn– X Ag( X = 1, 2, 5, 10 wt%) alloys were prepared by the rapid solidifi cation with copper-mold-casting technology. Phase analysis demonstrates that Fe–30 Mn– X Ag alloys consist of austenite γ phase with a fcc structure and martensite ε phase with a hcp structure. The yield strength of the samples increases with increasing Ag contents. Compared with Fe–30 Mn alloy, the degradation rates of Fe–30 Mn– X Ag in Hank's solution are signifi cantly improved. Cytotoxicity evaluation reveals that the Fe–30 Mn–1 Ag and Fe–30 Mn–2 Ag alloys perform less toxicity on the Human Umbilical Vein Endothelial Cells(HUVEC), while Fe–30 Mn–5 Ag and Fe–30 Mn–10 Ag alloys perform no toxicity on it. The contact angles of deionized water on the Fe–30 Mn– X Ag alloy surface were ranged from 55° to 69°, which is benefi cial to the adhesion and growth of the cells. Besides, the addition of Ag leads to a much lower M/H slope, particularly for the Fe–30 Mn–5 Ag alloy exhibiting a non-magnetic property as SS316 L. Therefore, the present Fe–30 Mn– X Ag alloys would be potential candidates for degradable metals.     

Effect of Cd and Sn Addition on the Microstructure and Mechanical Properties of Al-Si-Cu-Mg Cast Alloy

The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for AI-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy.On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd/Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd/Sn addition is due to the promotion of the θ‘phase.     

Mechanical Properties of Sintered Ce-Fe-B MagnetsEI北大核心CSCD

The (R, Ce)-Fe-B magnets have been successfully industrialized in recent years. The mechanical property of sintered permanent magnets is one important aspect of their comprehensive performances, which directly influences the service reliability and the production cost. In this work, the bending strength, fracture toughness, Vickers hardness and brittleness index of commercial (R1-xCex)(30.5 similar to 31.5)Fe-bal.-B1M1 (mass fraction, %) magnets with different Ce contents have been investigated. The microfractures of the magnets were observed by SEM equipped with EDS. It shows that the bending strength and the fracture toughness of (R, Ce)-Fe-B magnets have a downward tendency with increasing Ce content x, while the Vickers hardness of the magnets varies irregularly with Ce content. The optimum mechanical properties have been obtained in the (R1-xCex)(30.5 similar to 31.5)Fe-bal.-B1M1 magnet with x=0.15; the bending strength, fracture toughness and brittleness index of the magnet with x=0.15 are obviously superior to those of the ordinary sintered Nd-Fe-B magnets. Some flocculent oxide phases have been discovered in the (R, Ce)Fe-B magnet with x=0.15. The flocculent phases may absorb part of energy during crack propagating, and reduce the stress concentration at a crack tip, which is beneficial to strengthening and toughening of (R, Ce)-Fe-B magnets. However, the mechanical properties are obviously worse for the magnet with x=0.45 (Ce/SRE= 45%). That is probably because the microstructures of the magnet with x=0.45 become deteriorated, in which abnormally large grains have been observed. The results confirm that the fracture mechanism of sintered ( R, Ce)-Fe-B magnets with different Ce contents mainly appears intergranular fracture.     

Microstructure Control and High Temperature Properties of Al-Mn-Based AlloysEI北大核心CSCD

The process of production and working environment of heat exchangers call for materials with good elevated temperature properties. However, the previous investigations were mainly focused on their room temperature properties. The relationship between microalloying and high temperature properties, especially creep properties of Al-Mn-based alloys are barely discussed. In order to improve the industrial applications of Al-Mn-based alloys, the effect of Mg, Ni and Zr additions and annealing process on the microstructure and high temperature properties of Al-Mn-based alloys were studied in this work. The investigated alloys were treated in two ways, first one is cold-rolling and heat treatment at 873 K for 10 min, and the second one is cold-rolling, heat treatment at 623 K for 1 h and 873 K for 10 min. The results indicate that annealing process has remarkable effect on the grain shape, fine equiaxed crystal grains are obtained in the former, while stable elongated grains are obtained for precipitation precedes recrystallization at 623 K in the latter. With Mg addition, more AlMnSi phase precipitated during annealing. The addition of Zr and Ni increases the type and amount of heat resistant compounds, precipitate Al3Zr and AlMnSiNi, which are beneficial to improving high temperature properties of Al-Mn alloy. Al-Mn-0.3Mg-0.2Ni alloy has the best elevated temperature properties, and the tensile strength of it is 102 MPa (50 MPa higher than Al-Mn alloy) at 523 K. And the steady-creep rate is strongly decreased to 3.93x10(-8) s(-1), two orders of magnitude smaller than Al-Mn alloy at the temperature of 523 K under the stress of 40 MPa. With dispersoids complicated or increased, the movement of dislocations are pinned strongly, which are contribute to improving the creep properties of Al-Mn alloy for the creep is mainly controlled by dislocation climb.     

Influence of TiC Addition on Properties and Microstructure of Mo-Ti AlloyEI北大核心

Mo-Ti-TiC alloys were fabricated by powder metallurgy process through adding TiH2 powder and ultrafine TiC powder into Mo metal. The influence of the addition of nano-scale TIC particles on the microstructure and tensile properties of Mo-Ti alloy was studied. The results indicate that the tensile strength of Mo-Ti alloy was effectively increased by TiC particles addition. Mo-Ti with 0.05wt% TiC exhibited the highest tensile strength, which is 31.7% higher than that of Mo-Ti alloy. The addition of TiC protects Ti from oxidation, which is produced by decomposition and dehydrogenization of TiH2 particles. The second phase particles containing Mo, Ti, 0 and C in the alloy were formed with TiC addition. The grain size of the alloy decreased with the increase of the TIC content since the second phase particles can inhibit the grain growth.     

Effect of Strontium and Magnesium Additions on the Microstructure and Mechanical Properties of Al–12Si Alloys

Metals and Materials International - In this study, a binary Al–12Si, eight ternary Al–12Si–Sr, and six quaternary Al–12Si–0.1Sr–(0.2–1)Mg alloys were...     

Effect of Rare Earth on Microstructure and Properties of Pure Copper

Metallograph and scanning electron microscope studies of the distributionand function of rare earthmetals in copper show that RE can reduce the oxygen content,fine the grain Ceils of copper,and enhancethe mechanical and electrical properties.Excess RE in copper will lead to the formation of some RE com-pounds like Fe-Cu-RE and RECu_6.     

Effect of V–Ti Addition on Microstructure Evolution and Mechanical Properties of Hot-Rolled Transformation-Induced Plasticity Steel

In order to reveal the effect of V–Ti addition on the microstructure evolution and the mechanical properties of hot-rolled transformation-induced plasticity(TRIP) steel, two steels with 0.072 V–0.051 Ti steel(Bear-V–Ti steel) and 0.001 V–0.001 Ti steel(Free-V–Ti steel) were designed, respectively, and the comparison analyses were carried out by performing thermodynamic calculation and an experiment. With the thermodynamic calculation, the critical annealing temperature of a large fraction of retained austenite(～51%) obtained via solute enrichment was determined, and an optimized quenching at 650 °C and tempering at 200 °C adopted on the as-hot-rolled steel. The results show that the V–Ti TRIP steel displays more optimum mechanical stability during the tensile deformation, since the fraction and the mechanical stability of retained austenite are improved and the microstructure is also ultrarefined by V–Ti alloy precipitation. The yield strength of Bear-V–Ti steel increases from 650 to 800 MPa, and the ductility reaches 37%, showing that the comprehensive mechanical properties are greatly improved.     

Effect of Isothermal Temperature on Microstructure and Mechanical Properties of High Al–Low Si TRIP Steel

In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al–low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 °C and austempering temperature is 400 °C, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.     

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by In Situ Laser Directed Energy DepositionEI北大核心CSCD

以Ni粉与Ti粉为原料,采用激光定向能量沉积(LDED)技术制备NiTi形状记忆合金。利用XRD、物相拟合、SEM、EDS和DSC等测试方法,对NiTi合金的显微组织、物相含量和物相转变进行分析,随后采用压缩圆柱样品进行形状记忆效应测试,并评估其形状记忆效应。激光能量密度较低时,NiTi合金中产生大量Ni_(4)Ti_(3)相沉淀,随着激光能量密度增加,Ni_(4)Ti_(3)相消失。激光能量密度为20.0 J/mm^(2)时,NiTi合金具有2878 MPa的压缩断裂强度与34.9%的压缩失效应变,且样品在循环20 cyc后具有88.2%形状记忆恢复率。     

Study on Anisotropic Mechanical Properties of Cold Drawn Pearlitic Steel WireEI北大核心CSCD

Cold drawn pearlitic steel wires with ultra-high strength are widely applied in industrial fields such as bridge cables, automobile tire and springs rope. In recent years, the strengthening mechanism and microstructure evolution have been profoundly studied. In order to investigate the influence of microstructure evolution on mechanical properties, the anisotropic mechanical properties of cold drawn pearlitic steel wires were investigated by tensile test, SEM and TEM. Results indicated that the distinctions of tensile strength between three directions (parallel to the tensile axis, inclined to the tensile axis (45 degrees), vertical to the tensile axis) were amplified with increasing strain. The effect of strain strengthening was observed in parallel and inclined directions while the vertical direction remained strength stability in 1320 MPa. The wire rod was isotropic and the fracture mode was transgranular fracture; After cold drawing, the tensile strength reached peaks in parallel direction and valleys in vertical direction. The fracture mechanism of inclined and vertical directions remained transgranular or intergranular fracture while the fracture mechanism of parallel direction was converted into microvoid accumulation fracture. In TEM, the phenomenon was discovered that due to non-homogeneous distribution in vertical direction, dislocations piled up at the boundaries resulting in stress concentration. On the contrary, the dislocations were uniformly distributed which led to homogeneous transformation in parallel direction.     

Effect of Substrate Type and Temperature on the Tribological Properties of MoS_x Coatings

SPUTTERING deposited MoSx coatings are often usedas a solid lubricant in space applications,where a lowcoefficient of friction and long lifetime of coating areneeded.But the lubricating properties and endurancelives of sputtered MoSx coatings are strongly dependenton the sputtering parameters and the substrateconditions.Spalvin[1]showed that three groups can be dividedabout the effect of temperature on the nucleation ofMoSx coatings:(1)amorphous(-195°C);(2)crystalline-amorphous(-195°C …     

Effect of Nb and Mo on the Microstructure,Mechanical Properties and Ductility-Dip Cracking of Ni–Cr–Fe Weld Metals

A series of Ni–Cr–Fe welding wires with different Nb and Mo contents were designed to investigate the effect of Nb and Mo on the microstructure, mechanical properties and the ductility-dip cracking susceptibility of the weld metals by optical microscopy(OM), scanning electron microscopy, X-ray diffraction as well as the tensile and impact tests. Results showed that large Laves phases formed and distributed along the interdendritic regions with high Nb or Mo addition. The Cr-carbide(M_(23)C_6) was suppressed to precipitate at the grain boundaries with high Nb addition. Tensile testing indicates that the ultimate strength of weld metals increases with Nb or Mo addition. However, the voids formed easily around the large Laves phases in the interdendritic area during tensile testing for the weld metal with high Mo content. It is found that the tensile fractographs of high Mo weld metals show a typical feature of interdendritic fracture. The high Nb or Mo addition, which leads to the formation of large Laves phases, exposes a great weakening effect on the impact toughness of weld metals. In addition, the ductility-dip cracking was not found by OM in the selected cross sections of weld metals with different Nb additions. High Nb addition can eliminate the ductility-dip cracking from the Ni–Cr–Fe weld metals effectively.