316不锈钢因其优异的耐蚀和加工性能而得到广泛应用,但其宽泛的成分范围会导致性能波动。本文首先将置换型固溶合金化元素归类为稳定铁素体的类Cr元素（Cr,Si,Mo）和稳定奥氏体的类Ni元素（Ni,Mn）。进而引入“团簇加连接原子”模型,给出该不锈钢的16原子成分单元,由此将现有国标成分区间解析成五个16原子成分式,分别对应于两类元素的上下限（Cr,Si,Mo） 3.0625,3.5 -（Ni,Mn） 1.75,2.25 -Fe bal 和中值（Cr,Si,Mo） 3.25 -（Ni,Mn） 2 -Fe bal 。采用氩气保护电弧炉熔炼,用真空箱式炉实施均匀化处理（1150℃/2h,炉冷）,冷轧至5 mm薄片（变形量约50%）,再实施固溶处理（1050℃/0.5h,水淬）。类Ni元素含量最低的Ni 1.75 合金组织中出现铁素体相,对应的质量百分比成分区间为（21.2～18.5）(Cr,Si,Mo)-11.4（Ni,Mn）-Fe;其它三个样品均为单一奥氏体相。经固溶后,平均维氏硬度约为160,最高为174,均满足国标要求（低于200）。在质量分数为3.5%NaCl溶液中的电化学腐蚀实验结果表明,类Cr元素含量最高的Cr 3.5 -Ni 2.25 -Fe bal 合金（Fe-17.8Cr-0.6Si-2.7Mo-14.0Ni-0.8Mn-0.021C）体现出最强的耐蚀性能,成分式中类Ni元素原子个数在2以上的合金也表现出较强的耐蚀性,对应的质量百分比成分区间为（18.4～21.1）(Cr,Si,Mo)-（14.7～13.0）(Ni,Mn)-Fe。类Cr元素含量高的合金点蚀电位（0.211 V）也高。综上,Cr 3.25 -Ni 2 -Fe bal （Fe-16.7Cr-0.4Si-2.7Mo-11.9Ni-1.2Mn-0.021C）既能形成单相奥氏体,又具有满足标准要求的维氏硬度（～160HV）,并且其耐蚀性也在高的水平(自腐蚀电位-0.082 V、腐蚀电流密度1.83×10 -6 A·cm -2 、耐点蚀当量25.6、点蚀电位0.19 V),合金化元素含量适中,是最佳合金。
6种针刺工艺不同的碳纤维增强树脂基复合材料,其面内拉伸强度随着针刺密度和针刺深度的增大而降低,针刺处纤维的断裂使材料内的缺陷失稳扩展和面内纤维断裂,进而使材料整体拉伸失效.根据面内拉伸实验结果和纤维累计损伤理论并引入纤维体积折减系数,建立了分析针刺复合材料面内拉伸强度的理论模型.这个模型的预测结果与实验结果相符,并发现断裂纤维簇的个数与体积折减系数相关.用该模型可预报不同针刺工艺复合材料的面内拉伸强度,并指导设计针刺复合材料的预制体.
Thermal barrier coatings are widely used in the protection of engine turbine blade,in this paper,Ln2(Zr0.7Ce0.3)2O7(Ln=La,Nd,Sm,Gd)nanomaterials for the applications of thermal barrier coatings were synthesized by hydrothermal method,the crystallographic structures,morphologies and related ther-mophysical properties of powders and their bulk materials were comparatively assessed via various tech-niques.The analysis results of XRD and Raman spectra indicate that La2(Zr0.7Ce0.3)2O7,Nd2(Zr0.7Ce0.3)2O7 and Sm2(Zr0.7Ce0.3)2O7 are pyrochlore structures,while Gd2(Zr0.7Ce0.3)2O7 belongs to fluorite type.The lat-tice parameters,average particle sizes and specific surface areas were also characterized.The volume shrinkage/relative density,the sintering-resistance properties of the four bulk materials were evaluated by SEM observation.Additionally,their thermophysical properties(such as the activation energy of crys-tal growth,thermal expansion coefficient,and thermal conductivity)were investigated in detail.As the ionic radii of Ln decreasing,the activation energy of crystal growth and thermal expansion coefficient of Ln2(Zr0.7Ce0.3)2O7(Ln=La,Nd,Sm,Gd)increased,however the thermal conductivity is just the opposite.
The microstructure and tensile deformation behavior of different zones(base metal,heat affected zone and weld zone)of joints of P91 steel pipe before after 136000 hours of service as steam pipeline were comparatively studied by means of hardness tester,tensile tests at 25 and 545℃,metallos-copy,SEM and TEM+EDS etc.The results show that the hardness test results can reflect the degrada-tion behavior of tensile properties and the aging process of P91 steel joints.Compared with non-service steel pipes,the martensite decomposition and carbide coarsening behavior in each zone of welded joints of long-term serviced steel pipes obviously weaken the effect of martensite strengthening,precipitation strengthening and solution strengthening,and finally lead to the degradation of hardness,tensile proper-ties at room temperature and high temperature in each zone.Among others,the hardness of weld zone and the relevant room temperature-and high temperature-tensile properties are most significantly degrad-ed due to long-term service.The synergistic effect of the thermal cycling induced severe tempering dur-ing welding process with the long-term high temperature service may be an important cause for the signif-icant degradation of the mechanical properties of P91 steel pipe welds.
In order to solve the imbalance between strength and toughness in different cross sec-tions of a large size piston for hydraulic crushing hammer,the influence of heat treatment and microstruc-tural adjustmen/control on the microstructure and mechanical properties of 9CrV steel near-real shaped piston with a diameter of 190 mm was studied.The results show that when the piston were austenitized at 850℃ for 5 h and quenched at 230℃ for 4 h,then tempered at 230℃ for 4 h,the microstructure of a piston consists of bainite,bainite+troostite+residual austenite and pearlite respectively,from the sur-face to the core.The tensile strength of the piston surface layer is 1442 MPa,the impact absorbed ener-gy is 11 J,the impact toughness in the piston core part is poor,and the impact toughness is the lowest at 2/3 R of the piston.When the austenitizing temperature is decreased to 800℃ and tempering tempera-ture is increased to 400℃,the tensile strength of the piston surface layer increased to 1610 MPa,and the impact absorbed energy decreased to 7.4 J.The impact toughness of the piston core shows an increas-ing tendency,while the strength will decrease.When the piston is austenitized at 800℃ for 5 h and fol-lowed by quenching at 230℃ for 4 h,then tempering first at 230℃ for 4 h and then at 400℃ for 4 h,the tensile strength of the piston surface layer becomes 1672 MPa,the impact absorbed energy becomes 9.8 J.The impact toughness of piston core part has been improved,and the combination of strength and toughness of the piston tend to balance.It is found that with the lower austenitizing temperature a large number of undissolved carbide particles will be retained,it will hinder austenite growing,but refine grains.With the increasing tempering temperature,the dislocation tangles to pearlite ferrite will be restored,and the toughness of piston core can be improved.The carbon-rich residual austenite film in the bainite of pis-ton surface layer is stable.When it is tempered at 400℃,the carbide thin film will precipitate during the decomposition of residual austenite,which is easy to become a rapid crack propagation path and reduce the impact toughness.The residual austenite was transformed into lower bainite by tempering at 230℃ to prevent the formation of thin-film carbides by tempered at 400 ℃ to improve the impact resistance of pis-ton core,so that the toughness becomes balance in the different cross section parts of a piston.Based on the combination of optimizing and controlling of piston microstructure and heat treatment process,the strength and toughness of the piston are balanced.
Ferritic martensitic(F/M)steel is one of the main candidates for structural components of lead-bismuth fast reactors.Increasing the Si content can enhance the resistance of the material to Pb-Bis-muth corrosion,but it also affects the precipitation behavior of precipitates and mechanical properties of the material.In this paper,four ingots of F/M steels with different Si contents(0.9％,1.2％,1.5％and 1.8％by mass fraction)were vacuum melted and cast,and then forged to generate blocks,afterwards,the steels were subjected to the following heat treatment process:water cooling after solution treatment at 1050℃ for 30 min,and then air cooling after tempering at 760℃ for 90 min.The effect of the Si addi-tion on the precipitation behavior of precipitates and mechanical properties of 9Cr type F/M steel was carefully examined.The results show that the precipitated phases of 9Cr type F/M steel with different Si contents are M23C6,MX and Laves phases,and the presence of Si can promote the precipitation of Laves phase and M23C6 carbide.When the Si content is 0.9％～1.2％,the tensile strength and elongation of the steel are slightly reduced,and the impact performance remains stable;when the Si content is 1.2％～1.8％,the solid solution strengthening of Si and the precipitation strengthening of the precipitates make the strength of the steel increase,but with the increase of Si content,Laves phase and M23C6 type car-bide precipitates a lot,and the impact energy decreases significantly.
Fe76Si9B10P5 amorphous alloys annealed at 773～833 K with heterogeneous microstructure consisting of α-Fe,Fe2B and Fe3P phases,were de-alloyed in 0.05 mol/L H2SO4 solution.The porous structure was formed due to the preferential dissolution of α-Fe phase in the form of micro-coupling cells be-tween α-Fe phase and cathodic residual phases.The size of nanopores increased from 150 nm to 260 nm with the temperature increasing from 773 K to 883 K.The nanoporous Fe-Si-B-P electrode showed much superior redox performance compared with Fe76Si9B10P5 amorphous alloy,which was ascribed to its large specific area and more electrochemical active sites.
A composite of Z-scheme Ag3PO4/MIL-125(Ti)heterojunction was synthesized by loading Ag3PO4 nano particles on the surface of round-shaped MIL-125(Ti).The Ag3PO4/MIL-125(Ti)composite can effectively improve the utilization of light and charge separation efficiency.The crystal-structure,mor-phology,optical absorption,valence band structure and charge separation efficiency of the prepared Ag3PO4/MIL-125(Ti)composite were characterized by XRD、SEM、EDS、UV-vis、FTIR、EIS and PL testing methods.Under a simulated solar irradiation,the performance of Cr(Ⅵ)reduction by Ag3PO4/MIL125(Ti)composite with different deposition amounts of Ag3PO4 was studied.Furthermore,the effect of solution pH and catalyst dosage in the photocatalytic reduction process was also discussed.The photocatalytic test results indicated that the deposition of Ag3PO4 effectively improved the photocatalytic reduction per-formance of MIL-125(Ti).When the concentration of Cr(Ⅵ)solution was 10mg/L and pH was 2,the reduc-tion rate of Cr(Ⅵ)by Ag3PO4/MIL-125(Ti)-2 could reach to 96.9％.The results of bandgap structure calcu-lation and free radical trapping experiments show that photon-generated carriers in Ag3PO4/MIL-125(Ti)are conformed to Z-scheme mechanism.
The creep behavior at 130～240 MPa/973～1023 K of Sanicro25 steel for ultra-supercriti-cal power plants were investigated by OM,SEM and TEM.The results showed that the minimum creep rate increases with the increasing temperature and applied stress.Based on the characteristics of the minimum creep rate,the stress exponents of 7.6～8.2 and the apparent activation energy of 496.7～531.8 kJ/mol can be acquired for the creep process.Nano-scale Cu-rich phase and MX phase precipitat-ed in the matrix imped the dislocation motion,thus resulted in the emerging of creep threshold stress.The creep threshold stresses can be estimated by the linear extrapolation method,and which decrease with the increase in temperature.By invoking the concept of the threshold stresses to modify the constitu-tive equation,(ε)min=A2[(σ-σth)/G]nexp(-Q/RT),the normalization of the minimum creep rate can be acquired at various temperatures;Meanwhile,the true stress exponent(n=5)and the true apparent activation ener-gy(Q=286.6 kJ/mol approximately equal to the y-Fe self-diffusion activation energy)can be identified.The creep rate-controlling mechanism was determined to be dislocation climbing mechanism assisted by lattice self-diffusion.
The coarse-grained and fine-grained CuCr50 electrical contact materials were prepared by combining high-energy ball milling and spark plasma sintering(SPS)technology,and their composi-tion,density,microhardness and conductivity,the distribution of cathode spots on the surface of the con-tact during discharge,the speed of movement and the morphology of contact surface erosion were char-acterized,and the arc erosion characteristics of coarse-grained and fine-grained CuCr materials were studied.The results show that the hardness of fine-grained CuCr50 contacts(160.29HV)is higher than that of coarse-grained CuCr50 contacts(104.15HV),and the movement speed of cathode spots of fine-grained contacts is 16.9 m/s under 50 Hz power frequency conditions,which is 4.9％lower than that of coarse-grained contacts of 17.78 m/s.This suggests that the cathode spot on the surface of the coarse-grained contact moves slightly faster to the edge of the contact than the fine-grained contact.Compared with coarse-grained contacts,the cathode spots produced on the surface of the fine-grained contacts dur-ing arc burning are small in size,large in number,low in brightness and more uniform.Under the same current amplitude,the arc voltage drop of fine-grained CuCr contacts is lower than that of coarse-grained contacts.After arc ablation,the overall morphology of the fine-grained CuCr contact is flat,and there is no obvious large ablation pit and droplet splash.The comprehensive results show that the refinement of the second phase Cr phase can significantly improve the overall electrical contact performance of Cu-Cr50 contacts,and the arc ablation resistance of fine-grained CuCr50 contacts is higher than that of coarse-grained contacts.
7055-0.1Sc-T4 aluminum Al-alloy plates of 11 mm in thickness were firstly subjected to friction stir welding(FSW)and then the effect of post-weld heat treatment on the microstructure and me-chanical properties of the FSW joints was investigated.The results show that for the as welded FSW joints,the hardness profiles distribution exhibited"W"shaped pattern with the low hardness zone(LHZ)on both the retreating(RS)and the advancing sides(AS),respectively.And the joints fractured at the LHZ on RS with the strength coefficient are 63.0％-73.8％.After the post-weld artificial aging at 120℃ for 12 h(AA),the hardness of the nugget zone(NZ)increased but the hardness of the LHZ,tensile proper-ties and fracture location were unchanged.Solution treatment at 535℃ for 1.5 h+water quenching+artifi-cial aging at 120 ℃ for 12 h(T6)did not change the grain structure of the joint under low welding speed of mm/min,but caused the abnormal grain growth at the bottom of the NZ under high welding speed of 250 mm/min.Moreover,T6 heat treatment resulted in the dissolution of the original precipitates and the re-precipi-tation of fine and uniform η'and η(MgZn2)phases,and therefore significantly improved the hardness of the joints.The T6 joint cracked along the"S"line during tension with a seriously reduced plasticity and joint efficiency of 87％.
用真空热压法制备不同B4C颗粒尺寸(7 μm、14 μm、20μm)的15％B4C/Al-6.5Zn-2.8Mg-1.7Cu复合材料,研究了增强颗粒尺寸对其微观组织和力学性能的影响.结果表明,在这三种复合材料中B4C颗粒均匀分布,B4C-Al界面反应较为轻微,未见明显的界面反应产物.三种复合材料基体中沉淀相的尺寸基本相同(约为5.5 nm).B4C颗粒的尺寸对复合材料力学性能有较大的影响.B4C颗粒尺寸为7 μm的复合材料性能最佳,屈服强度为648 MPa,抗拉强度为713 MPa,延伸率为3.3％.随着颗粒尺寸的增大复合材料的强度和延伸率均降低.对三种复合材料的强化机制和断裂机制的分析结果表明:小尺寸B4C颗粒增强的复合材料强度较高,颗粒在变形过程中不易断裂,因此其塑性较好.
用选区激光熔化(SLM)技术制备多孔石墨烯/钛复合材料,研究了石墨烯(Gr)作为增强相对其微观结构、力学性能以及抗腐蚀性能的影响.结果表明:用SLM制备的多孔钛由较小的等轴晶组成,石墨烯加入使其晶粒尺寸进一步减小,石墨烯没有在Ti基体中团聚,部分石墨烯与Ti原位生成的TiC产生了弥散强化.多孔Gr/Ti复合材料的压缩曲线由弹性变形阶段、应力平台阶段和致密化阶段组成,其硬度、抗压强度和压缩率分别为503HV、317.38 MPa和42％;其抗腐蚀性能高于纯钛,腐蚀电位为-0.325 V,腐蚀电流密度为3.28×10-7A·cm-2.
分别用熔融法和烧结法制备P2O5-Nb2O5-BaO-Na2O-CeO2体系磷酸盐微晶玻璃,用XRD谱和SEM观察表征其结构并测定其体积密度、显微硬度、介电性能、极化性能和储能特性,研究了制备工艺对其结构和性能的影响.结果表明,用熔融法可制备出结构更致密的微晶玻璃,使其体积密度和显微硬度提高和降低其介电损耗.当CeO2添加量提高到1％(摩尔分数)时,用两种工艺都可实现微晶玻璃的结构致密化,并促进其结晶.结晶程度的提高可改善微晶玻璃的介电常数和极化性能.用熔融法制备的CeO2添加量为1％(摩尔分数)的微晶玻璃样品其能量释放密度为13.5 mJ/cm3、储能效率为50.1％.
以Cu-C拼接靶为靶材,用高功率脉冲磁控溅射制备出4种Cu含量(原子分数)低于10％的Cu掺杂非晶碳(a-C:Cu)薄膜,研究了Cu含量对a-C:Cu薄膜组分结构、电学性能以及载流子输运行为的影响.结果表明:随着非晶碳中Cu含量的提高,a-C:Cu薄膜中sp2-C的含量提高、团簇尺寸增大、薄膜电阻率、透过率和光学带隙均减小,费米能级向价带偏移.Cu含量为2.77％和3.88％的样品在150～250 K的载流子输运机制为Mott型三维变程跳跃传导,在250～350K则为热激活传导;而Cu含量(原子分数)为5.4％和7.28％的样品在150～350 K均为Mott型三维变程跳跃传导.掺入Cu,可控制非晶碳薄膜的光学和电学性能.
用微弧氧化(MAO)和磁过滤阴极真空弧离子镀(FCVAD)在Zr-2合金表面制备ZrO2/Cr复合膜,用热重分析仪(TGA)评估了Zr-2合金基体和ZrO2/Cr复合膜在900～1100℃蒸汽环境中的抗氧化性能,并分析其氧化后氧化层的截面结构、相组成和成分深度分布.结果表明,在900、1000和1100℃蒸汽环境中分别氧化3600 s后,ZrO2/Cr复合膜试样单位面积增重约为Zr-2合金基体的3/8、1/4和2/5.在高温蒸汽环境中,ZrO2/Cr复合膜表面氧化生成的致密Cr2O3膜能抑制氧向内扩散,提高锆合金的抗蒸汽氧化性能,阻止锆试样在1000℃蒸汽环境中出现分离氧化.ZrO2/Cr复合膜的表面Cr层完全消耗前,Cr涂层的氧化主要取决于铬向外扩散,而不是氧向内扩散.在蒸汽氧化过程中,MAO膜的中间层能抑制氢渗透进入锆合金基体.
用场发射扫描电镜(FE-SEM)和透射电镜(TEM)观察一种第四代镍基单晶高温合金长期时效和持久断裂后的微观组织和位错组态,研究了这种合金在1000℃和1130℃长期时效过程中的组织演化和在1100℃/140 MPa条件下的持久性能.结果表明:这种合金具有较好的组织稳定性,在1000℃长期时效过程中γ'相逐渐长大,但是在1000h后仍有较好的立方度且没有TCP相析出.在1130℃长期时效500h后γ'相发生连接和筏化;时效200 h后开始析出TCP相,时效1000 h后合金中TCP相的面积分数只有0.04％.在1130℃长期时效500 h后,γ/γ'界面形成位错网并随着时效时间的延长变得更加规则致密.这种合金在1100℃/140 MPa条件下的持久寿命为676.5 h,达到第四代镍基单晶高温合金水平.持久断裂后γ'相发生N型筏化,合金中析出针状TCP相(μ相)并在TCP相附近出现位错塞积.在持久试验过程中,合金中生成的γ/γ'界面位错网和a<010>超位错有利于提高其持久性能.
使用长50m的落管研究Ni-Cr-Al-W-Ta镍基单晶高温合金在重力(1g)和微重力(μg)条件下的凝固行为.用金相显微镜(OM)观察合金的凝固组织并用图像分析软件测量和统计一次和二次枝晶间距,使用扫描电镜能谱(SEM-EDS)测定不同位置枝晶干与枝晶间的化学成分并计算微观偏析系数.结果表明,在重力和微重力条件下这种合金的枝晶特征和合金元素的微观偏析明显不同.重力样品一次和二次枝晶间距比微重力样品的大,随着凝固距离的增大一次枝晶间距的差异变大,而二次枝晶间距的差距变化不大.随着凝固的进行,微重力样品枝晶间Ta、Cr和Al元素的含量呈现先明显升高后略微降低的趋势,W元素含量呈现逐渐下降的趋势,枝晶间液相的密度呈现略微降低的趋势.重力样品枝晶间Ta、Cr和Al元素含量的分布趋势与微重力样品基本相似,W元素含量的分布则与微重力样品明显不同,大部分凝固阶段呈上升趋势,使枝晶间液相的密度沿逆重力方向提高.上述结果表明,在重力条件下凝固前沿溶质密度差导致的对流作用微弱,不是造成枝晶间距增加的主要原因,主要原因应该与凝固前沿热对流造成的温度梯度的降低有关.
用高温煅烧、反应合成以及光还原等方法制备新型g-C3N4/Ag/BiOBr复合光催化材料,使用SEM、XRD、EPMA、FT-IR、XPS和UV-vis等手段对其表征,研究了这种复合材料在金卤灯照射下对硝酸盐氮(50mg/L)的还原效果和氮气选择性.结果表明,使用1 g/Lg-C3N4/Ag/BiOBr复合光催化材料,光反应180min后硝酸盐的去除率为95.2％.用g-C3N4/Ag/BiOBr光催化硝酸盐氮的主要产物中N2的占比最高(为88.0％),氮气的选择性为92.4％.g-C3N4/Ag/BiOBr催化剂中的Ag能促进对电子的捕捉,BiOBr的光生电子经银单质转移到g-C3N4的价带上形成Z型复合光催化结构.这种复合光催化剂可将硝酸盐氮氧化,空穴清除剂甲酸在复合材料中空穴的作用下转化成强氧化性物质(COO-)并进一步将其还原成硝酸盐氮.
对喷射成形M3高速钢进行不同制度的热处理,使用OM、SEM、TEM、EDS、XRD以及硬度测试等手段研究了这种钢在淬、回火过程中的组织和硬度变化以及硬度偏低问题.结果表明,随着淬火温度的提高组织中的M6C型碳化物百分占比呈降低的趋势,而MC型碳化物的百分占比只有在淬火温度高于1200℃时才稍有降低;在淬火温度不高于1230℃的条件下仍能保证组织中碳化物尺寸细小且均匀分布.组织中的MC型碳化物成分分布的不均匀与其生成和工艺的雾化过程相关.随着淬火温度由1200℃提高到1230℃,钢的回火硬度显著提高.淬火温度的提高使MC型碳化物的溶解量提高,可有效解决喷射成形高速钢硬度偏低的问题.
