Effect of ECAP processing on distribution of second phase particles,hardness and electrical conductivity of Cu-0.81Cr-0.07Zr alloy

The effect of equal-channel angular pressing(ECAP)processing at room temperature and 300℃on the distribution of the second phase particles and its influence on hardness and electrical conductivity of the commercial Cu-0.81Cr-0.07Zr alloy were investigated.Microstructural characterization indicated that the area fraction of coarse Cr-rich particles decreased after ECAP processing.This reduction was attributed to the Cr dissolution induced by plastic deformation.The electrical conductivity of the alloy decreased by 12%after 4 ECAP passes at room temperature due to the increase of electrons scattering caused by higher Cr content in solid solution and higher density of defects in the matrix.These results were supported by the reduction of the Cu lattice parameter and by the exothermic reactions,during differential scanning calorimetry(DSC)analysis,observed only in the samples subjected to ECAP processing.Aging heat treatment after ECAP processing promoted an additional hardening effect and the complete recuperation of the electrical conductivity,caused by the re-precipitation of the partially dissolved particles.The better combination of hardness(191 HV)and electrical conductivity(83.5%(IACS))was obtained after 4 ECAP passes at room temperature and subsequent aging at 380℃for 1 h.

Monte Carlo study on abnormal growth of Goss grains in Fe-3%Si steel induced by second-phase particles

The selective abnormal growth of Goss grains in magnetic sheets of Fe-3%Si （grade Hi-B） induced by second-phase particles （AlN and MnS） was studied using a modified Monte Carlo Ports model. The starting microstructures for the simulations were generated from electron backscatter diffraction （EBSD） orientation imaging maps of recrystallized samples. In the simulation, second-phase particles were assumed to be randomly distributed in the initial microstructures and the Zener drag effect of particles on Goss grain boundaries was assumed to be selectively invalid because of the unique properties of Goss grain boundaries. The simulation results suggest that normal growth of the matrix grains stagnates because of the pinning effect of particles on their boundaries. During the onset of abnormal grain growth, some Goss grains with concave boundaries in the initial microstructure grow fast abnormally and other Goss grains with convex boundaries shrink and eventually disappear.

Phase-field study of the second phase particle effect on texture evolution of polycrystalline material

The second phase particle effect on texture evolution of polycrystalline material is studied through phase-field method. A unique field variable is introduced into the phase-field model to represent the second phase particles. Elastic interaction between particles and grains is also considered. Results indicate that in the presence of second phase particles the average particle diameter turns smaller than in the absence of these particles and retards texture formation by pinning effect. The second phase particles change the strain energy profile, which tremendously influences the pinning effect.

Grain growth simulation with the second phase particle pinning for heat-affected zone of microalloyed steel welds

The second phase particle dispersed in microalloyed steel has different effects on grain growth depending on their size and volume fiaction of the second phase particles which will change during welding thermal cycles. The particle coarsening and dissolution kinetics model was analyzed for continuous heating and cooling. In addition, based on experimental data, the coupled equation of grain growth was established by introducing limited size of grain growth with the consideration of the second phase particles pinning effects. Using Monte Carlo method based on experimental data model, the grain growth simulation for heat-affected zone of microalloyed steel welds was achieved. The calculating results were well in agreement with that of experiments.

CALCULATION OF SECOND PHASE PARTICLE-GRAIN BOUNDARY INTERACTION RANGE

On the basis of the grain boundary equation by HeUman and corresponding analysis of Worner, this article deals with the interaction range between the second-phase particle （SPP） and grain boundary （GB） as viewed from the applicability of grain boundary equation. Also, a new expression describing the interaction range has been derived, which solves the problem in theory that the interaction range between SPP and GB can only be qualitatively analyzed previously. It is shown that given the interaction position between SPP and GB, the interaction range can be quantitatively determined by use of this expression.

退火工艺对Zr-Sn合金TREX管坯SPPs及腐蚀行为的影响研究

文章对Zr-Sn系锆合金中间工序管坯采用两种退火工序制备,采用扫描电镜(Scanning Electron Microscope,SEM)对其微观组织形貌进行观察,并对其第二相尺寸进行统计,最后对其腐蚀性能进行分析。SPPs统计结果表明,退火工序的选择对SPPs的尺寸形貌有显著影响,A样品内析出相的数量明显多于样品B,且尺寸相对较大。腐蚀结果表明,采用A工序退火的TREX管坯更耐均匀腐蚀。

Interface conjunction factors of the second phase particles in alloys and their effects

The second phase in multi-phase alloys has connection with many important phenomena such as aging strengthening,dispersion strengthening,secondary hardening,crystal refinement.In this paper,the interface conjunction factors of the interface between MC(M=V,Nb,Ti) and austenite and martensite are calculate out.The relationship between these factors and the characteristics are analyzed.The reason for the second phases being fine and dispersing and their strengthening and toughening effect on the alloy is explained using the relationship.Based on the relationship,the valence electron structure of the interface between the second phase particles and the matrix can be optimized by changing the alloying elements,which make it possible to design the composition of alloys from the valence electron structure of the second phase particles.

Kinetics of Precipitation Behavior of Second Phase Particles in Ferritic Ti-Mo Microalloyed Steel

Two types of stress relaxation tests were carried out to investigate the incubation time for incipient precipi-tation of Ti（C,N） in deformed austenite and （Ti,Mo）C in ferrite of ferritic Ti-Mo microalloyed steel The size dis-tribution, amount and chemical composition of precipitates were obtained by using physicochemical phase analysis, and calculated according to thermodynamics and kinetics. The experimental results demonstrated that the incubation time was reduced with increasing Ti content, and prolonged with the addition of Mo. After 30 % deformation at 850 ℃, the nucleation of strain-induced Ti（C,N） was a relatively slow process. On the other hand, the temperature where the nucleation rate of （Ti, Mo）C in ferrite was the highest descended first and then ascended with increasing Ti content, and so did the temperature where the incubation time was the shortest. The key point is that the tempera-ture of steel containing about 0.09 % Ti is the lowest. The mass fraction of MC-type particles with size smaller than 10 nm in steel containing 0.09% Ti and 0.2% Mo reached 73.7%. The size distributions of precipitates in steel containing 0.09% Ti were relatively concentrated compared with that in steel containing 0.07% Ti.

Microstructural characteristics and second-phase particles in yttrium-bearing Fe-10Ni-7Mn martensitic steels

In this study, the microstructure and second-phase particles in yttrium （0.05 wt.%and 0.8 wt.%） bearing Fe-10Ni-7Mn steels were characterized. The results of X-ray analysis as well as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy indicated the formation of （Fe, Ni, Mn）17Y2 precipitates with hexagonal structure in a Fe-10Ni-7Mn-0.8Y （wt.%） alloy. Lattice parameters of these precipitates were calculated as follows：a=0.8485 nm and c=0.8274 nm. Formation of Y2O3 sub-micron particles was also confirmed in both yttrium bearing steels via electrolytic phase extraction method. The effect of these precipitates on the prior austenite grain size was investigated. The results revealed that these precipitates had an effective role in controlling the prior austenite grain size.

Improvement of warm formability of Al-Mg sheet alloys containing coarse second-phase particles

Several alloying elements involving Zr, Cu, Zn and Sc were added to Al-Mg sheet alloys in order to obtain an excellent combination of high strength and good high-temperature formability. Microstruc-tural examination showed that coarse intermetallic particles were formed in the microstructure and their amounts changed with variations of the alloying elements. During warm rolling of thermome-chanical treatments prior to warm deformation, the coarse particles initiated cracks, decreasing the warm formability. For healing the crack damage and further improving the warm formability, a process of hot isothermal press was developed and optimized to the sheet alloys. With this process, the biaxial stretch formability at 350℃ was improved by 22% for an aluminum alloy containing a large amount of coarse particles.

Grain growth in a nanostructured AZ31 Mg alloy containing second phase particles studied by phase field simulations

Phase field models were established to simulate the grain growth of a nanostructured AZ31 magnesium alloy,which contain spherical particles of differing sizes and volume fractions, under realistic spatial and temporal scales.The effect of the second phase particles on the nanostructure evolution was studied. The simulated results were compared with those of the conventional microstructured alloy.The expression of the local free energy density was improved by adding a second phase particle term. The right input parameters were selected for proper physical meaning. It was shown that the rules that govern the pinning effect of the second phase particles during the grain growth were different for the nanostructure and microstructure. There was a critical particle size value that affected the grain growth within the nanostructure. If the particle size was lower than the critical value, the pinning effect on grain growth increased with decreasing particle size. When the particle size was greater than the critical value, the particles had almost no pinning effect.However, in the conventional microstructured material,the larger particle size resulted in an enhanced pinning effect during grain growth for particle sizes smaller than 1 μm. The effect was reversed when the particle size was larger than the critical value. For the nanostructure, the critical value was200 nm when the particle content was 10 v.%, and the critical value decreased when the content increased. When the particle size was 30 nm, the particle pinning effect on the grain growth increased for increasing particle content.

CONTINUUM VOID NUCLEATION MODEL FOR Al-Mg ALLOY SHEET BASED ON MEASURED PARTICLE DISTRIBUTION

Void nucleation within measured particle fields of an aluminum alloy is investigated to develop a continuum nucleation model which reflects nucleation at the individual particle scale. A nucleation model for heterogeneous particle distributions is synchronized with the continuum model of Chu and Needleman using the average nucleation strain. The parameters in the continuum model are identified from the particle fields and are evaluated over the range of stress states observed in sheet metal forming. The synchronized continuum nucleation model achieves very good agreement with the nucleation trends for three measured particle fields in uniaxial tension, plane strain, and equal-biaxial tension.

锆合金压力电阻焊接头热影响区中第二相的组织特征

采用热模拟试验机分别对Zr-4合金管和锆锡铌(Zr-Sn-Nb)系锆合金管与Zr-4合金柱进行压力电阻焊连接,研究了接头热影响区的第二相形貌、成分和晶体结构,并与母材进行对比。结果表明:在压力电阻焊的热力耦合作用下,Zr-4合金接头热影响区近熔合线区的第二相粒子发生完全溶解,近母材区的密排六方结构Zr(Fe,Cr)_(2)Laves第二相颗粒的数量相比母材显著减少,平均直径增大。Zr-Sn-Nb系合金接头热影响区近熔合线区的第二相颗粒数量很少,以直径小于50nm的体心立方结构β-Nb相为主,近母材区的第二相颗粒数量介于母材与热影响区近熔合线区之间,由细小的体心立方结构β-Nb相以及粗大的面心立方结构(Zr,Nb)Fe_(2)相组成。

预处理对汽车车身结构件用6061铝合金型材性能的影响

采用电子万能试验机、硬度计及导电仪等设备研究了不同预处理温度对汽车车身结构件用6061铝合金型材性能的影响。结果表明:在120~270℃时,随着预处理温度的升高,材料的硬度和强度都呈现出先升高后降低的趋势,而材料的电导率则呈现出先降低再升高的趋势。经过预处理后的材料其自然时效现象消失,材料的硬度、强度及电导率可在很长一段时间的自然停放过程中保持稳定。220℃×1 h和270℃×1 h的预处理使基体组织中析出了大量粗大第二相粒子,该类粒子大大降低了基体的过饱和固溶度,进而使材料人工时效后的力学性能显著恶化。120℃×1 h和170℃×1 h的预处理不对后续人工时效后材料的力学性能产生影响。

氮含量与终轧温度对钛微合金化高强钢CGLC700低温冲击韧性的影响

针对钛微合金化高强钢CGLC700低温冲击韧性差的问题,通过热力学计算与高温原位观察,采用电子背散射衍射、透射电镜、扫描电镜和光学显微镜对含Ti高强钢的夹杂物、第二相粒子、断口形貌和低温冲击韧性等进行了研究。结果表明,含Ti高强钢低温冲击韧性差的原因与钢中大尺寸脆性夹杂物和Ti(C,N)、TiN析出相有关。将钢中w[N]从0.0049%降低至≤0.0035%时,可以有效降低钢中脆性夹杂物的数量和尺寸,从而提高钢材冲击韧性;终轧温度从885~895℃降低至875~885℃,可以促使纳米级TiC第二相粒子析出和大角度晶界的生成,并降低有效晶粒尺寸,从而明显改善钢材的低温冲击韧性;同时降低氮含量至≤0.0035%与终轧温度在875~885℃时,钛微合金化高强钢中平均晶粒尺寸从3.1μm降至2.7μm,小尺寸有效晶粒占比高,大尺寸夹杂物及数密度降低,大角度晶界中占比增长了16.6%,钢材低温冲击功可以从14.75 J提高到37.35 J。

Zirlo合金和M5合金的微观组织和微区成分

利用高分辨透射电子显微镜和能谱仪对Zirlo合金和M5合金进行了微观组织和微区成分分析。结果表明:M5合金中圆球状的第二相弥散分布在晶界上和晶粒内,尺寸约为50 nm;第二相的主要成分为Zr元素和Nb元素,第二相为体心立方结构的β-Nb相;在Zirlo合金中弥散分布着两种尺寸不同的第二相粒子,一种为体心立方结构的β-Nb,尺寸为20~40 nm;另一种为密排六方结构的Fe_(2)Nb_(0.4)Zr_(0.6)相,尺寸约为100 nm。

退火工艺对电池壳用钢XDCK第二相粒子影响的研究

为了研究退火工艺对电池壳用钢XDCK第二相粒子的影响,在连续退火条件下对XDCK进行模拟试验和工业试验。采用连续退火模拟试验机模拟连续退火生产工艺,对不同退火温度和退火保温时间试样中第二相粒子的尺寸、数量和分布情况进行研究。结果表明电池壳用钢XDCK中第二相粒子为TiC,随着退火温度的升高和保温时间的延长,第二相粒子尺寸逐渐增大。

旋转速度对滚动摩擦沉积增材组织的影响

滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,利用金相显微镜、扫描电子显微镜对不同旋转速度增材试件宏观形貌、微观组织进行了表征。结果表明:(1)沉积层组织致密,无夹杂、裂纹等缺陷、相邻两沉积层之间形成良好的冶金结合。(2)沉积层呈现细小的轴晶粒组织,随着旋转速度升高,晶粒尺寸呈下降趋势。(3)沉积层第二相粒子呈现点片状分布于Al基体上,随着转速增大,第二相粒子趋向于细化与均匀。

溶质元素在含Nb海工钢中析出行为的热力学研究

采用ThermoCalc软件计算了超高强含Nb海工钢的相转变规律和第二相粒子析出规律,并将计算结果与实验结果进行对比。计算结果表明,在平衡状态下,该材料基体为铁素体相,含有的析出相主要包括Nb(C,N)相(FCC-A1#2)、BN相(BN-B4),富Mo相(HCP-A3#2)、富Cu相(FCC-A1#3)和碳化物相(M23C6-D84)。Nb(C,N)相在1171.5℃开始析出,在800℃时的析出量为0.056%,提高C、Nb元素含量会显著促进Nb(C,N)相的析出;富Mo相在700.4℃开始析出,在400℃时的析出量为0.34%;富Cu相在675.8℃开始析出,在400℃时的析出量为0.88%;碳化物相在647.7℃开始析出,在400℃时的析出量为0.9%。通过与实验结果对比可知,调质态实验钢在室温时组织由回火马氏体(BCC相)组成。在TEM下,仅观察到Nb(C,N)相,未发现BN相、富Mo相、富Cu相和碳化物相。

焊后热处理对核反应堆压力容器用16MND5钢组织和性能的影响

采用光学显微镜、透射电子显微镜,通过拉伸、冲击和落锤试验等方法研究了焊后热处理温度和保温时间对16MND5钢的组织和力学性能的影响。结果表明:经模拟焊后热处理后16MND5钢的室温和350℃抗拉强度和屈服强度都呈下降趋势,且下降幅度随焊后热处理温度的升高和保温时间的延长而增大;焊后热处理时间的延长导致钢的冲击性能小幅度下降,焊后热处理温度对冲击性能的影响并不明显;焊后热处理后的钢基体中弥散分布的细小第二相粒子数量减少、尺寸增大,导致钢的强度降低。