焊后热处理对T92/HR3C异种钢接头组织和力学性能的影响

以Inconel 82焊丝为填充金属,采用手工钨极惰性气体保护焊对T92/HR3C异种钢进行焊接,经焊后热处理后,采用光学显微镜、透射电镜对接头各区的微观组织进行表征,并对接头的室温拉伸性能进行测试。结果表明,接头T92钢热影响区(HAZ)由板条马氏体和部分等轴亚晶粒组成,板条晶界上存在连续的M₂₃C₆碳化物,晶内碳化物溶解;HR3C钢HAZ组织表现出较高的热稳定性;焊缝金属由较粗大的奥氏体枝晶和M₂₃C₆碳化物组成,同时存在一定量的位错;接头室温拉伸断裂发生在HR3C钢侧熔合区附近的焊缝,呈现为韧性断裂。     

焊接热循环对Ni-Fe基合金高温力学性能的影响

采用焊接热模拟试验,分析了焊接热循环对一种700℃超超临界火电机组高温部件候选材料——Ni-Fe基高温合金组织和高温性能的影响.结果表明,焊接热循环过程使合金中γ'相以及MC碳化物大量固溶.700℃持久试验中HAZ试样在400 MPa的持久断裂时间低于母材,300和350 MPa的持久断裂时间与母材相当.随着持久试验进行,HAZ组织中的晶界逐渐析出M₂₃C₆,晶内重新析出大量γ'相,使HAZ的持久性能逐渐恢复.高温焊接热循环使MC发生部分溶解,为M₂₃C₆在后续持久试验时效中的析出提供了C元素.     

GH3230合金M23C6型碳化物的析出行为

研究了固溶态GH3230合金在800~1100 ℃时效不同时间下的碳化物析出行为。结果表明:GH3230合金固溶态组织主要为γ相+初生粒状碳化物M₆C+少量晶界粒状碳化物M₂₃C₆。试验合金在800~1100 ℃短时时效后,晶界和晶内析出的碳化物主要为M₂₃C₆型。其中晶界粒状M₂₃C₆型碳化物有沿着晶内长大的倾向,并逐渐变成胞状碳化物。在同一时效温度下,晶内碳化物析出数量会随着时效时间的增加而增加,此后会逐渐回溶,回溶开始的时间会随着时效温度的提高而逐渐提前。     

C-HRA-3耐热合金850 ℃持久性能及组织特征

研究了C-HRA-3耐热合金在850 ℃持久试验过程的碳化物特征。结果表明:当持久应力为120 MPa时,持久寿命为37.8 h,主要析出相包括M₂₃C₆相和Ti(C, N)相,高应力状态下,M₂₃C₆相沿变形带析出。当持久应力为80 MPa时,持久寿命延长至491 h,晶界处M₂₃C₆相部分回溶,导致晶界特征不明显,同时细小M₂₃C₆相重新析出,晶内析出的Ti(C, N)相尺寸增加。不同应力下试样的断裂方式均为沿晶断裂,裂纹源优先在尺寸较大的析出相(M₂₃C₆和Ti(C, N))周围萌生,导致伸长率随持久寿命延长而减小。     

高温长时服役HR3C钢焊接接头的组织与性能

采用金相显微镜、扫描电镜、X射线衍射仪以及拉伸和弯曲试验研究了高温服役4.2万小时超超临界机组用HR3C钢焊接接头的微观组织和力学性能。研究结果表明,高温长时服役后HR3C钢焊缝金属中形成了大量条状和颗粒状M₂₃C₆析出相,焊接热影响区奥氏体晶粒长大,在晶界附近形成了板状M₂₃C₆相。拉伸和弯曲试验结果表明HR3C钢焊接接头高温服役后表现出明显的时效脆化倾向。     

时效时间对S30432钢组织的影响

利用扫描电镜、透射电镜研究了S30432钢在650 ℃不同时效时间处理后的微观组织演变。结果表明,未经时效的S30432钢组织为均匀奥氏体,晶内有很多未溶的大片状一次Nb（C,N）和细小的二次Nb（C,N）,M₂₃C₆型合金碳化物极少;300 h时效后组织出现明显回复过程,有少量的富铜相和M₂₃C₆型碳化物的析出;时效1000 h后,富铜相和M₂₃C₆碳化物数量急剧增加,M₂₃C₆颗粒逐渐长大并呈链状分布。随时效时间延长,孪晶逐渐消失。TEM照片显示,随着时效时间的延长,富铜相颗粒长大,并和M₂₃C₆相、孪晶一起阻碍位错运动,提高了S30432钢的高温性能。     

超高合金粉末钢热处理过程中碳化物的演变对其耐蚀性能的影响

使用扫描电镜(SEM)、X射线衍射(XRD)、Image-J图像处理软件等研究了轧制态超高合金粉末钢在热处理过程中不同阶段的碳化物演变行为。结果表明：轧制态超高合金粉末钢的组织主要由铁素体、马氏体基体和M₂₃C₆、M₇C₃及MC 3种类型碳化物组成。随着热处理的进行,碳化物的平均尺寸和最大尺寸以及团聚状碳化物的数量呈现出先降低-后增加-再降低-再增加的变化趋势,碳化物的数量则表现为先降低-后增加-再降低的变化趋势;M₂₃C₆型碳化物随着热处理温度的升高其含量逐渐减少,在1000℃等温3 h后,M₂₃C₆型碳化物大部分分解回溶,在降温阶段该型碳化物再次析出;在整个热处理过程中MC型碳化物几乎没有发生变化,M₇C₃型碳化物没有发生向M₂₃C₆型碳化物的转变;随着热处理的进行,超高合金粉末钢耐蚀性表现为先升高-后降低-再升高-再降低...     

固溶处理对53Cr21Mn9Ni4N耐热钢组织及碳化物的影响

利用FactSage软件中的FSstel数据库对53Cr21Mn9Ni4N耐热钢的相图进行计算,分析了氮元素对凝固及冷却过程中相变及析出相的影响,得到了53Cr21Mn9Ni4N耐热钢平衡凝固及冷却相变路径图,并用OM、SEM、XRD、EDS等对53Cr21Mn9Ni4N耐热钢在1200 ℃固溶3、10、20、40和60 min后的显微组织及碳化物演变规律进行了研究。结果表明,53Cr21Mn9Ni4N耐热钢由1600 ℃平衡冷却至300 ℃的过程中完整的平衡相变路径为:液相+气体→液相→液相+δ铁素体→液相+δ铁素体+奥氏体→液相+奥氏体→奥氏体→奥氏体+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体+σ相。M₂₃C₆的析出温度随着氮含量的增加而降低,M₂(C,N)的析出物温度随着氮含量的增加而升高,M₂₃C₆会因M₂(C,N)的析出受到抑制。53Cr21Mn9Ni4N耐热钢的铸态组织非常不均匀,奥氏体呈树枝晶状生长,枝晶间析出大量层片状碳化物。随着固溶时间的增加,分布在枝晶间的层片状碳化物逐渐变成块状及短棒状,碳化物的数量逐渐减少,粗壮的树枝晶也逐渐变得细小。53Cr21Mn9Ni4N耐热钢在1200 ℃固溶后的组织及碳化物均得到明显改善。     

蠕变过程中P91钢晶界析出相的变化行为

对600℃和650℃蠕变持久断裂试验过程中P91钢组织演变及晶界析出相的变化规律进行了研究。结果表明，在蠕变过程中，P91钢马氏体板条组织随蠕变断裂时间增加逐渐趋于分散，晶界析出相的数量及尺寸增加。晶界上的析出相主要为M₂₃C₆相和Laves(Fe₂Mo)相，Laves相的形核点主要位于晶界上M₂₃C₆相界面处，晶界上的M₂₃C₆相与基体相比具有更高含量的Mo,为Laves相的形成和粗化提供了有利条件，同时晶界上偏聚的Si增加了钢的自扩散系数，促进了Laves相的形成，也使得Laves相的粗化速率较M₂₃C₆相更高。在蠕变过程中P91钢的硬度随断裂时间的延长呈下降趋势，且试验温度越高硬度下降越明显。     

K439B铸造高温合金800℃长期时效组织与性能演变

对K439B合金开展800℃、3000 h长期时效,研究合金显微组织及力学性能的演变,分析室温拉伸及815℃、379 MPa持久性能的变形机制。结果表明：热处理态K439B合金中的γ’相呈球状,晶界存在MC及M₂₃C₆ 2种碳化物,而枝晶间仅存在MC碳化物。在800℃长期时效过程中,γ’相的粗化遵循Ostwald熟化机制且形貌趋于立方化,γ′相粗化速率为71.7 nm³/h;晶界和枝晶间MC碳化物发生退化,M₂₃C₆碳化物析出含量逐渐增加。时效3000 h后晶界γ’相与M₂₃C₆碳化物存在■的位向关系。热处理态合金的室温抗拉强度和屈服强度分别为1159.0和911.5 MPa,815℃、379 MPa持久寿命为150.4 h。长期时效后γ’相尺寸增加使得位错的运动方式由以位错在基体中滑移为主向位错切入γ′相为主转变,γ′相中出现了更多的堆垛层错,合金室温拉伸强度和815℃、379 MPa持久寿命均降低。     

Effect of boron and carbon on the fracture toughness of IN 718 superalloy at room temperature and 650 °C

The effect of B and C microadditions on the fracture toughness of IN 718 superalloy was investigated at room temperature (RT) and at 650 °C. At RT, the fracture toughness was observed to increase with increasing B and C concentrations. C had a relatively weak effect on the fracture toughness at 650 °C, but the influence of B was significant. At RT the highest fracture toughness value was obtained for the alloy with 29 ppm B and 225 ppm C at RT, and at 650 °C the alloy with 60 ppm B and 40 ppm C had the highest fracture toughness. An increase in the concentration of B to 100 ppm, however, resulted in a reduction in the fracture toughness at 650 °C. Fractographic observations showed that the formation and coalescence of microvoids was the predominant fracture mechanism at RT. In contrast, at 650 °C, the fracture surface exhibited intergranular cracking in the alloy with lower B concentrations and transgranular cracking coupled with fine dimples in the alloy with higher B concentrations. It is suggested that B impedes intergranular cracking by increasing the cohesion of grain boundaries and improving the grain boundary stabilization. The RT increase in the fracture toughness of the material caused by the addition of C is attributed to the formation of intergranular and intragranular carbides that increased the resistance to the plastic deformation.     

Microstructures And Mechanical Properties Of In-Situ Al2o3/Tial Composites By Exothermic Dispersion Method

In-situ Al2O3/TiAl composites were fabricated by pressure-assisted exothermic dispersion （PAXD） method from elemental powder mixtures of Ti, Al, TiO2, and Nb2O5. The microstructures and mechanical properties of the as-sintered composites are investigated. The results show that the as-sintered products consist of γ-TiAl, α2-Ti3Al, Al2O3, and NbAl3 phases. Microstructure analysis indicates that Al2O3 particles tend to disperse on the grain boundaries. Application of a moderate pressure of 35 MPa at 1200℃ yields Al2O3/TiAl composites with fine Al2O3 reinforcement and a discontinuous network linking by Al2O3 particles. The aluminide component has a fine submicron γ ＋α2 lamellar microstructure. With increasing Nb2O5 content, Al2O3 particles are dispersed uniformly in the matrix. The hardness of the composites increases gradually, and the bending strength and fracture toughness of the composites reach to the maximum value, respectively.     

Mechanical alloying of dispersion-hardened Ni3Al-B from elemental powder mixtures

Mechanical alloying and hot extrusion were studied as a means to dispersion harden an intermetallic compound based on Ni ₃ Al- B from elemental powder mixture. The oxide used for the dispersoids was partially stabilized zirconia. During mechanical alloying the microstructure evolved according to the characteristic stages found in other mechanical alloying systems. Completion of the alloying reaction required 16 h, beyond which loss of the crystalline property set in. Experimental observation of the grain refinement during mechanical alloying agreed with a prediction based on an existing model. Compared to V- cone mixing, the mechanical alloying produced a homogeneous distribution of fine dispersoids. The refined grain structure and dispersoids resulted in a high tensile yield strength over a wide range of temperatures.     

Microstructural Analysis of TiAl x N y O z Coatings Fabricated by DC Reactive Sputtering

TiAl _x N _y O _z coatings were prepared by DC reactive sputtering on AISI D2 tool steel substrates, using a target of Ti-Al-O fabricated from a mixture of powders of Ti (22.60 wt.%), Al (24.77 wt.%), and O (52.63 wt.%). The coatings were deposited on substrates at room temperature in a reactive atmosphere of nitrogen and argon under a pressure of 8.5 × 10⁻³ mbar. X-ray diffraction, electron dispersive spectroscopy, Raman scattering, and nanoindentation techniques were employed to investigate the coatings. The results show that the increment in the nitrogen flow affects the structure and the mechanical properties of the coatings. The sample with the lowest nitrogen flow presented the highest hardness (10.5 GPa) and the Young’s modulus (179.5 GPa). The hardness of the coatings TiAl _x N _y O _z as a function of crystalline grain size shows a behavior consistent with the Hall–Petch relation.     

Effect of SI Content on the Oxidation Resistance of Ti3Al1-x Si x C2 (x⩽ 0.25) Solid Solutions at 1000–1400°C in Air

The oxidation behavior of Ti₃Al_1-x Si _x C₂ (x ⩽ 0.25) solid solutions was investigated in flowing air at 1000–1400°C for up to 20 hrs. Similar to Ti₃AlC₂, Ti₃Al_1-x Si _x C₂ (x⩽ 0.15) solid solutions display excellent oxidation resistance at all temperatures because of the formation of the continuous α-Al₂O₃ protective layers. However, Al₂(SiO₄)O formed during oxidation of Ti₃Al_1-x Si _x C₂ (x=0.2 and 0.25) solid solutions at and above 1100°C, which is believed to be responsible for the deterioration of oxidation resistance of Ti₃Al_0.75Si_0.25C₂ at 1300°C. Additionally, Ti₅Si₃ was also found in the oxidized samples. This implies that Ti₅Si₃ precipitated from Ti₃Al_1-x Si _x C₂ solid solutions during oxidation. But it has been proven that Ti₅Si₃ has little effect on the oxidation resistance of the material, which is attributed to an interstitial carbon effect.     

Polarization study on doped lanthanum gallate electrolyte using impedance spectroscopy

Alternating current complex impedance spectroscopy studies were conducted on symmetrical cells of the type [gas, electrode/La_1−x Sr _x Ga_1−y Mg _y O₃ (LSGM) electrolyte/electrode, gas]. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The electrodes selected for this investigation are candidate materials for solid oxide fuel cell (SOFC) electrodes. Cathode materials include La_1−x Sr _x MnO₃ (LSM), La_1−x Sr _x Co _y Fe_1−y O₃ (LSCF), a two-phase particulate composite consisting of LSM and doped-lanthanum gallate (LSGM), and LSCF + LSGM. Pt metal electrodes were also used for the purpose of comparison. Anode material investigated was the Ni + Ce_0.85Gd_0.15O₂ composite. The study revealed important details pertaining to the charge-transfer reactions that occur in such electrodes. The information obtained can be used to design electrodes for intermediate temperature SOFCs based on LSGM electrolytes. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

炭/炭复合材料表面氢刻蚀改善等离子体渗Cr层的抗氧化性能

用双层辉光等离子渗金属技术,在炭/炭复合材料表面制备Cr涂层,改善其抗高温氧化性能。渗Cr前先用微波等离子体对炭/炭复合材料表面进行氢刻蚀处理,提高Cr涂层与基体间的结合力。用扫描电子显微镜、能谱仪和X-射线衍射仪分别对刻蚀、渗Cr及氧化后炭/炭复合材料表面形貌、成分及组织结构进行分析。结果表明:经过900℃、1 h刻蚀后,炭/炭复合材料表面形成蜂窝状结构,经后续950℃、2 h渗Cr处理后,在刻蚀后的炭/炭复合材料表面形成厚约5μm的Cr/Cr_yC_x复合涂层,涂层表面致密均匀,无裂纹和剥落;900℃高温循环氧化2.4 h后的失重率为2.79%,抗高温氧化能力较基材得到明显改善。     

Magnetic phase diagram of CrTe1−xSbx (0.0≤x≤1.0)

Measurements of the high field magnetization of CrTe_1−xSb_x (0.0≤x≤1.0) were carried out at 4.2 K in pulsed magnetic fields up to 300 kOe. The temperature dependence of the magnetization of CrTe_1−xSb_x was measured in the temperature range from 4.2 K to 800 K. The magnetic phase diagram of CrTe_1−xSb_x (0.0≤x≤1.0) was determined, which is similar to the typical one for the mixed crystals of the layered antiferromagnetic and ferromagnetic compounds proposed by de Gennes.     

Microstructure of a plasma-sprayed Mo-Si-B alloy

Powders of Mo₅₂Si₃₈B₁₀ were plasma sprayed under inert conditions onto stainless steel substrates to determine if high density free standing forms could be synthesized by this process. Thermal spray conditions were varied to minimize porosity and oxygen impurities while minimizing evaporative metal losses. The assprayed and sintered microstructures were characterized using scanning and transmission electron microscopy and quantitative x-ray diffraction (XRD). The as-sprayed microstructure consisted of elongated splats tens of microns in length and only one to three microns in thickness. The splats contained submicrometer grains of primarily MoB and Mo₅Si₃B _x (T1) and minor amounts of MoSi₂ and a glassy grain boundary phase. The interior of the splats typically consisted of a fine eutectic of MoB and T1. Small pieces were cut out of the cross section of the sample and pressureless sintered for 2, 6, and 10 h at 1800 °C in flowing Ar. After sintering for 2 h at 1800 °C, the samples exhibited a coarser but equiaxed microstructure (1 to 5 μm grain size) containing 78 vol.% T1, 16 vol.% MoB, and 6 vol.% MoSi₂ as determined by XRD. Approximately 8 at.% of the Si formed silica. The high-temperature anneal removed all vestiges of the layered structure observed in the as-sprayed samples.     

Self-propagating high-temperature synthesis with post-heat treatment of La1−xSrxFeO3 (x = 0–1) perovskite as catalyst for soot combustion

La_1−xSr_xFeO₃ (x = 0–1) perovskite, Sr-substituted LaFeO₃, was prepared by Self-propagating high-temperature synthesis (SHS) and its catalytic activity for soot combustion was experimentally examined in comparison with that of a conventional Pt/Al₂O₃ catalyst. The products were also characterized by XRD, FE-SEM, and BET specific surface area. The XRD analysis revealed that all the products had a perovskite phase as the major compound, together with intermediate phases with higher x values (x = 0.7–1). The BET specific surface area of the products increased with x. Moreover, the catalytic activity for soot combustion also increased with x, wherein the BET specific surface area appeared an appropriate index for explaining the observed activity. The sample with x = 0.8 exhibited the highest activity for soot combustion among all the SHS products. The soot combustion temperature of this product was as much as 100 °C lower than that of non-catalytic soot combustion. In other words, it had the same activity as that at only 20 °C higher, in comparison to conventional Pt/Al₂O₃ catalyst. More significantly, average apparent activation energy of sample with x = 0.8 calculated by Friedman method using TG/DTA was approximately 15 kJ/mol lower than that of Pt/Al₂O₃ catalyst. This result suggested that La_1−xSr_xFeO₃ has the possibility to be an alternative catalyst to Pt/Al₂O₃ catalyst.