Nonequilibrium grain-boundary segregation and ductile-brittle-ductile transition in Fe-Mn-Ni-Ti age-hardening alloy

Nonequilibrium segregation kinetics of alloying elements and a ductile-brittle-ductile transition behavior have been investigated in an Fe-8.4Mn-7.4Ni-l.7Ti alloy. The alloy experienced a ductilebrittle-ductile (DBD) transition during isothermal aging. In the brittle region, the alloy showed a decrease in intergranular fracture strength and a subsequent increase with aging time. This is due to the segregation of titanium to the grain boundaries and its desegregation into the matrix. The intergranular fracture strength was higher on the zero tensile elongation finish curve than on the start curve. This is because the grain-boundary segregation level of titanium is relatively lower on the finish curve. The lowest intergranular fracture strength increased with increasing aging temperature, which was attributed to a lower grain-boundary segregation level of titanium at higher temperature. Manganese caused an overall reduction in intergranular fracture strength and, as a result, the delayed occurrence of the zero tensile elongation (ZTE) finish curve in a temperature and log-time plot. formerly Graduate Student, Department of Metallurgical Engineering, Seoul National University, Seoul, 151-742 Korea     

高温时效对S31042钢管室温拉伸性能的影响

研究了700℃0～3 000 h时效对Φ57 mm×9.7 mm S31042无缝钢管(%:0.06C、0.35Si、1.18Mn、24.50Cr、20.54Ni、0.40Nb、0.23N)室温拉伸性能的影响。结果表明,0～1 000 h时效时,随时效时间的增加,S31042钢屈服(R_p0.2)和抗拉强度(R_m)迅速增加,但钢的伸长率(A)和断面收缩率(Z)急剧降低;当时效时间超过1 000 h,各项性能变化趋缓;随时效时间增加,室温拉伸断口由含丰富韧窝的韧性断口逐渐过渡到沿晶脆性断口;0～1000h时效随时效时间增加,晶界处Cr₂₃C₆相迅速增多,超过1 000 h时效,析出相的变化不明显。     

5083合金不同均质制度的组织和性能研究对比

采用光学金相显微镜、拉伸试验机、SEM及EDS等分析手段,对比分析5083合金不同均质制度下微观组织、力学性能及拉伸断口形貌.研究结果显示,5083合金均质处理后,枝晶组织消除,初生相部分回溶到基体中,弥散相均匀析出,起到一定的弥散强化作用,强度和塑性均优于铸态;未均质铸锭以脆性断裂为主,均质处理的铸锭断裂方式为韧性断...     

高能超声波处理高硅铝硅合金的组织和力学性能

采用高能超声波对Al-20%Si合金进行熔体处理,研究超声波处理对Al-20%Si合金微观组织形貌及其力学性能的影响。结果表明,在660℃温度下,对Al-20%Si合金熔体进行高能超声波处理,可以使铝硅合金的初晶硅形貌由粗大的板片状逐渐变成细小的球状颗粒,圆整度高,分布均匀,并且使其抗拉强度和延伸率提高。通过对合金拉伸断口形貌的观察,发现在经过超声处理的Al-20%Si合金断口上有较多的撕裂带和韧窝,表现为脆性断裂和韧性断裂的混合型断口。     

Microstructure and mechanical properties of spray-deposited Al-17Si-4.5Cu-0.6Mg wrought alloy

High Si content in Al-Si alloys usually leads to the formation of coarse, brittle Si phase under slow solidification conditions. In the present study, an Al-17Si-4.5Cu-0.6Mg (referred to hereafter as AS17) was synthesized using spray deposition to modify the Si phase. In the spray deposition process, the master alloy of AS17 was atomized using N₂ gas, and was deposited on a collecting substrate directly into a three-dimensional material. The microstructure and mechanical behavior of the spray-deposited AS17 were studied using optical microscopy (OM) scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, and tensile tests. The present results indicate that in the spray-deposited AS17, the eutectic Si phase was modified from a “flakelike” morphology, characteristic of ingot metallurgy (IM) materials, into a “particulate” morphology. The formation of the coarse primary Si blocks was suppressed. Moreover, the size and morphology of Si particulates were found to have significant influences on the deformation behavior. During plastic deformation, extensive fracture of Si occurred. The percentage of fractured Si increased with the increasing amount of plastic deformation and the size of Si particulates. Finally, the room-temperature mechanical properties of the spray-deposited AS17 were compared with its IM counterpart A390 (an IM alloy with identical composition as AS17). The strength and ductility of AS17 were improved over those of A390. In the T6 condition, the yield strength and tensile elongation of AS17 were 503 MPa and 3.0 pct, respectively, whereas those of A390 were 374 MPa and 1.3 pet, respectively.     

不同轧制及退火处理0.1C-5Mn中锰钢的氢脆敏感性

 尽管中锰钢的强塑性等力学性能得到了较大幅度提升,但要大规模地应用于汽车部件制造,仍需解决材料在制造和服役过程中面临的氢脆等系列难题,在此背景下,利用电化学充氢、氢热分析仪、慢应变速率拉伸试验机及扫描电镜等研究了两种不同状态(热轧和温轧)0.1C 5Mn中锰钢在650 ℃保温30 min(两相区退火处理)后的氢脆敏感性。结果表明,热轧和温轧退火样的微观组织分别为板条状及等轴+板条状的铁素体与奥氏体的复相组织。尽管温轧退火样的强度比热轧退火样提高了约150 MPa,伸长率降低了约5%,但两者的强塑积均可达到约33 GPa·%。两种试验材料充氢时吸附的氢绝大部分为对应低温逸出峰的可扩散性氢,温轧退火试验材料的氢脆敏感性低于热轧退火钢。充氢热轧退火样断口起裂处的断裂机制为穿晶断裂+沿原奥氏体晶界的脆性沿晶断裂;温轧退火样的起裂处则为空心韧窝+包括奥氏体(变形后转变为马氏体)晶粒的实心韧窝,后者实际上为沿着奥氏体和铁素体界面起裂的一种脆性沿晶断裂。造成两种试验材料氢脆敏感性不同的原因主要是其微观组织及其所引起的氢致断裂方式的差异。     

Factors affecting the intergranular hydrogen embrittlement of Co3Ti

The influence of intergranular hydrogen embrittlement on the mechanical behavior and fracture behavior of Co₃Ti and 0.1 wt% B-doped Co₃Ti compounds were studied. The significant environmental effect was investigated at ambient temperatures. The elongation and tensile strength showed lower values in the sequence of vacuum, air and hydrogen conditions though the yield strength was insensitive to the environment. The remarkable strain rate dependence was also investigated. As the strain rate decreased, the elongation and tensile strength decreased in a sigmoidal form and again the yield strength remained constant. The decreases of the elongation and tensile strength were investigated with decreasing test temperature below 400°C at the lower strain rate. These embrittlements were severer in the nearstoichiometric alloys of Co-23 at.% Ti than in the off-stoichiometric alloys of Co-21 at.% Ti. The addition of 0.1 wt% B did not actually affect the mechanical behavior of undoped Co₃Ti compounds. Fracture behavior was fairly consistent with the mechanical behavior; there was a change in fracture mode from the transgranular fracture mode, through a mixed mode, to the intergranular fracture mode as the strain rate decreases, by the alternation from vacuum to hydrogen conditions and as the Co atoms become excess. The reduction of ductility and tensile strength occurred in the present Co₃Ti compound was suggested to be due to hydrogen-assisted intergranular embrittlement. The dynamic and atomistic mechanism by which the cohesive strength of grain boundary was affected by the hydrogen was proposed as the probable explanation.     

轻质Al-Mg-Li合金的微观组织与力学性能

采用熔炼和热挤压制备轻质Al-5.5Mg-2.0Li-0.1Zr-0.2Sc合金,利用X射线衍射仪、差示扫描量热仪、金相显微镜、扫描电子显微镜、显微硬度计及拉伸试验机对合金的物相组成、微观组织、力学性能及断口形貌进行检测分析,研究时效工艺温度（120 ℃和160 ℃）对合金微观组织和力学性能的影响.结果表明:Al-Mg-Li合金挤压后晶粒组织呈纤维状,存在一定数量的Al₃Li（δ′）和Al₂MgLi（S）相;经固溶和时效处理后,再结晶晶粒尺寸变大,主要析出相为δ′相S相;160 ℃时效处理容易加速时效析出行为,导致析出相粗化,强化效果减弱;经120 ℃/20 h峰时效处理后,合金的抗拉强度、屈服强度和延伸率分别达到532 MPa、475 MPa和4.4 %.      

硅含量对喷射成形铝硅复合材料显微组织与力学性能的影响

利用双喷嘴扫描喷射成形技术制备27%SiAl、42%SiAl、50%SiAl等3种Si-Al合金电子封装材料,并对该材料进行热等静压致密化处理。研究合金沉积态和热等静压态的显微组织,测定合金的热膨胀系数、抗拉强度及抗弯强度,利用扫描电镜研究其断裂机制。结果表明:沉积态Si-Al合金的硅相呈均匀弥散分布。随含硅量增加,合金凝固区间增大,初生硅相的数量增多,平均尺寸增大,由全部颗粒状分布逐渐演化为呈部分颗粒、部分骨架状分布,这种均匀弥散分布的结构有利于降低合金的热膨胀系数。27%SiAl、42%SiAl、50%SiAl合金的热膨胀系数连续可控,室温至200℃分别为14.76×10 6、9.75×10 6、9.29×10 6/K。随硅含量升高,材料的抗弯强度和抗拉强度呈下降趋势。27%SiAl合金的平均抗拉强度和抗弯强度分别达到196 MPa和278 MPa,伸长率为9.5%。42%SiAl与50%SiAl的平均抗拉强度与抗弯强度都接近,分别达到140 MPa及220 MPa,伸长率小于1%。断裂方式由以铝相的韧性断裂为主逐渐转变为以硅相的脆性裂为主。     

退火温度对冷轧中锰钢组织性能和断裂行为的影响

 为了系统研究临界区退火和全奥氏体区退火对中锰钢性能的影响,为中锰钢的实际应用提供理论基础,在650~900 ℃范围内系统研究了冷轧中锰钢的显微组织和力学性能,并通过断口形貌观察分析了试验钢的断裂特性。结果表明,试验钢在临界区退火的综合力学性能明显优于全奥氏体区退火。650~750 ℃退火时,抗拉强度在1 000 MPa左右,强塑积超过30 GPa·%,发生韧性断裂,宏观上可以观察到明显的层状裂纹,微观下为大量韧窝;在800~900 ℃退火时,抗拉强度在743~1 154 MPa范围内波动较大,强塑积不足10 GPa·%,断口平整,发生脆性沿晶断裂;退火温度为650 ℃时,组织为片层状和等轴状的奥氏体、铁素体双相及大量渗碳体;随着退火温度的升高,渗碳体逐渐溶解消失,等轴状组织所占体积分数明显增加,奥氏体体积分数也不断增加,在750 ℃时达到52.2%;退火温度为800 ℃时,有马氏体产生,奥氏体体积分数下降;退火温度为900 ℃时,组织基本为马氏体,残留奥氏体体积分数仅为14.6%。     

Influence of Powder-Chip Based Reinforcement on Tensile Properties and Fracture Behaviors of LM6 Aluminum Alloy

Tensile properties and fracture behaviors of silicon rich LM6 aluminum alloy were investigated in details for as cast alloy and modified by LM6 powdery-chip capsules. The obtained results showed that 20% modified LM6 cast composite ensured the excellent tensile properties (tensile strength of 203 MPa with 3.8% elongation). An impressive increase in the elongation (6.8%) was found for 25% modified cast composite with good ultimate tensile strength, 6.2% higher than unmodified (182 MPa). Characterization of the casts and fracture surfaces were carried out to study the effect of reinforcement particles. An influence of un-melted chip structure was observed inside the cavities and on fractured surfaces. The XRD results showed that cast consisted of inter-metallics of AlO₂, Al₂Si and Al₄Si. It was attributed to micro-cracks prevalently propagated along the broken eutectic silicon particles and some rejected solid particles on the fractured surfaces with ductile and inter-granular fracture. Debonding and cracking of silicon particles were also detected on the fractured surface of the specimens.     

含硫易切削模具钢高温热塑性行为探讨

为研究易切削模具钢高温热塑性,利用热膨胀仪分析了该材料在不同冷速下的微观组织转变规律及相变点,并绘制了CCT曲线;利用Gleeble-3800试验机模拟研究材料高温拉伸断裂行为,结合断口形貌分析材料热塑性规律。试验结果表明,该材料高温热塑性存在明显的3个区域,分别为第3脆性区、韧性区和第1脆性区。试验钢在950~1 150 ℃范围内变形性能最优,为高温塑性区;950 ℃以下为第3脆性区,断口形貌为韧窝和解理,且随着变形温度的升高,韧窝数量增多,伸长率增加,直至950 ℃拉伸后断口形貌基本上全为韧窝;1 300 ℃及以上为第1脆性区,伸长率随变形温度升高而下降。提高冷却速率,会增加冷却过程中奥氏体内部的热应力,导致在相同温度下变形时伸长率较低冷却速率时小。     

粉末冶金Cu-15Ni-8Sn合金时效组织的演变行为

对粉末冶金Cu-15Ni-8Sn合金进行热挤压、固溶处理后,研究400℃时效不同时间对合金力学性能及其组织的影响。结果表明:随时效时间延长,Cu-15Ni-8Sn合金的抗拉强度先升高后降低,伸长率先降低后升高,合金断裂方式表现为由沿晶断裂为主向穿晶断裂为主转变。合金抗拉强度在400℃时效1.5 h时获得最大值918MPa。综合考虑合金的强度和韧性,400℃的最佳时效时间为2 h。借助扫描电子显微镜和透射电子显微镜研究合金在400℃时效不同时间(1~3 h)的组织结构变化及其对合金强度和塑性的影响,结果表明:在欠时效阶段,合金组织在富Sn区出现了有序排列的介稳态DO22相,基体的FCC结构开始向DO22有序化结构转变,合金强度大幅提升。而在峰时效阶段,DO22向L12转变,合金强度继续增加,随片层状不连续析出组织开始由晶界向晶内生长,合金强度下降。在过时效阶段,DO22进一步向L12转变,并且片层状不连续析出组织开始大肆侵蚀基体调幅组织,导致合金强度降低,塑性提高。在时效后期,调幅组织被片层状组织大幅侵蚀,出现片层状组织粗化并断裂的现象,粒状γ相(DO3)不断生成,由于这一过程需要更大的浓度起伏而进行得非常缓慢,合金组织仍以大量片层结构为主,因而合金强度和塑性变化不明显。     

碳含量对Fe-Mn-Cu-C系TWIP钢组织和力学性能的影响

 采用真空熔炼法制备Fe-20Mn-3.0Cu-XC系高强度高塑性合金钢,通过X射线衍射（XRD）、光学显微镜（OM）和透射电子显微镜（TEM）观察方法研究了碳含量对该系列合金微观组织和力学性能的影响,分析了合金的拉伸变形微观机制。结果表明：Fe-20Mn-3.0Cu-XC系合金拉伸变形前后均为单相奥氏体组织,未发生马氏体相变。随着碳质量分数的增加,合金的屈服强度、抗拉强度和伸长率均显著提高。Fe-20Mn-3.0Cu-1.41C合金的屈服强度为501.62MPa,抗拉强度为1178.4MPa,具有优异的综合力学性能。Fe-20Mn-3.0Cu-XC系合金具有优异的应变硬化能力。随着碳质量分数增大至1.41%,最大应变硬化指数n值达到0.782。Fe-20Mn-3.0Cu-XC系合金拉伸变形过程中,TWIP效应是主要的塑性变形机制,大量位错的塞积、形变孪晶的形成以及位错与孪晶间的交互作用共同引起材料强度和塑性的提高。     

烧结温度对内燃机用TiZrVMo高熔合金组织和力学性能的影响

运用放电等离子烧结方法(SPS)制备TiZrVMo合金,并通过控制不同的烧结温度获得了不同力学特性与组织结构的试样。测试结果表明,对合金烧结处理后其基体中形成了包含BCC与FCC两种晶体结构,BCC组织形成了比FCC组织更高的衍射峰。当烧结温度增加后,晶粒尺寸呈现增大的现象,塑性先增大后降低。经过1100℃烧结得到的试样压缩屈服强度为1501.4MPa,塑性应变31.4%。随着烧结温度的增加,屈服强度先减少后增加,塑性应变先增大后减小。当烧结温度上升后,合金材料从准脆性断裂逐渐转变为微孔聚集型断裂,之后形成了大尺寸晶粒并发生沿晶断裂的现象,呈现脆性解理断裂的特点。     

退火时间对Ti?6.0Al?3.0Zr?0.5Sn?1.0Mo?1.5Nb?1.0V钛合金组织及力学性能的影响

针对近α型Ti?6.0Al?3.0Zr?0.5Sn?1.0Mo?1.5Nb?1.0V新型钛合金,在退火温度740 ℃的基础上,研究了退火时间对其组织与力学性能的影响。结果表明:经过3次真空自耗电弧炉熔炼,三火热轧后得到的板材组织由初生α相基体及β转变组织组成的部分再结晶组织和加工态组织等组成。随着退火时间的增加,退火板材的显微组织均以初生α相为主,且α相所占的比例从81.73%逐渐增加至85.61%,组织中长条状α相逐渐破碎球化,等轴α相开始均匀化、粗化。随着退火时间的增加,退火板材的延伸率逐渐增加,抗拉强度先降低再增加然后又降低,屈服强度先增加后降低,显微硬度先增加后降低。退火时间为1 h时,板材的断口由滑移带、涟波、小等轴韧窝组成,断裂方式为韧性断裂,退火时间大于等于2 h时,板材的断口完全由等轴韧窝组成,断裂方式为韧性断裂。最佳退火工艺为740 ℃退火2 h,此时板材的抗拉强度、屈服强度、延伸率和显微硬度分别为:984 MPa、941 MPa、15.27%、HV 347.67。研究结果对高强耐蚀钛合金退火工艺的制定有指导作用,为解决钛合金在实际生产中遇到的问题提供了科学依据。      

Al-3Si-0.6Mg-(Cu,Mn)合金薄板的组织性能

采用拉伸试验、金相、扫描电镜、透射电镜高分辨组织分析方法,研究了水冷铜模铸造的扁锭轧制的Al-3.0Si-0.6Mg-0.4Cu-0.6Mn-0.18Fe合金薄板经400℃至540℃不同温度保温30 min水淬、室温停放90 d(自然时效)后的组织和性能.结果表明:在6009合金基础上提高Si的质量分数至3%,有提高其强度的作用;该合金薄板经540℃×30 min固溶处理自然时效后屈服强度为180 MPa、抗拉强度为313 MPa、延伸率接近23%,其组织中存在Si结晶相及含Fe、Mn和少量Cu、Si的结晶相,以及尺寸小于0.5μm的以含Mn为主并含少量Si和Fe的弥散相;提高其固溶处理温度至540℃,合金薄板的强度明显提高,其原因是析出强化产物尺寸增大,密度提高了.     

Effect of Additive Cu10Sn Alloy on Sintering Behavior of Elemental Powders in Composition of 465 Stainless Steel

 The addition of Cu 10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering time, and the mass percent of Cu 10Sn. For vacuum sintering, effective sintering occurs at temperature between 1 250 ℃ and 1 300 ℃. The maximum sintered density was achieved at 1 300 ℃ for 60 min with 3% (in mass percent) Cu 10Sn alloy. More than 3% (in mass percent) Cu 10Sn content and temperature above 1 300 ℃ caused slumping of the samples. A maximum density of 74 g/cm3 was achieved with 3% (in mass percent) Cu 10Sn content at a sintering temperature of 1 300 ℃ for 60 min. A maximum ultimate tensile strength (UTS) of 517 MPa was achieved with 3% (in mass percent) Cu 10Sn content. With content higher than 2% (in mass percent) Cu 10Sn, a maximum increase in the density was observed. The fracture morphologies of the sintered samples are also reported.     

时效温度对K487合金组织和性能的影响

 研究了不同时效温度对K487合金组织和性能的影响。结果表明,随时效温度提高,合金组织中γ′相尺寸增大,针状μ相减少,不规则块状和条状μ相边缘尖角变圆钝,合金强度下降,塑性提高。经900 ℃×5 h时效后,合金可获得较好的综合性能,其屈服强度约685 MPa,伸长率和断面收缩率分别达到105%和155%。     

600 MPa级低合金高强钢的组织调控与工艺优化

为了开发并稳定600 MPa级低合金高强钢的生产工艺参数,利用连续退火模拟机对试验钢进行了连续退火试验,并通过扫描电镜和拉伸试验机研究了均热温度和过时效温度对试验钢显微组织和力学性能的影响。结果表明,随着均热温度的升高,试验钢的屈服强度和抗拉强度均逐渐减小,伸长率逐渐增大;随着过时效温度的升高,屈服强度逐渐增大,抗拉强度逐渐减小,伸长率则先增大后减小。试验钢在820 ℃均热、390 ℃过时效时,获得最优的力学性能,其中抗拉强度为627 MPa,屈服强度为493 MPa,总伸长率超过20%。此外,利用透射电镜观察到钢中存在大量的纳米尺度析出物,这些析出物对试验钢强度的提升有较大的贡献。