烧结温度对铁基粉末冶金航空刹车材料组织的影响

铁基粉末冶金刹车材料是飞机上常用的一种刹车材料,通常采用加压烧结工艺制得,在烧结工艺中,烧结温度是最为关键的参数之一.该文作者研究了烧结温度(900,930,950,980和1 020 ℃)对其显微组织、致密化的影响以及由此引起的力学性能(硬度、抗压强度和抗弯强度)的变化.借助于材料组织结构及理论分析,阐述了该材料组织结构、力学性能变化的原因.研究表明:在烧结温度由900 ℃增至930 ℃的过程中,铁由体心立方结构的α-Fe全部转变为面心立方的γ-Fe,碳在γ-Fe中的扩散系数比其在α-Fe中的扩散系数低,使铁、碳合金化程度降低,然而,原子间互扩散系数增加,以及碳在γ-Fe中的溶解度比在α-Fe中的溶解度增大,使烧结得以进行,它们的综合作用则使材料密度、硬度和强度缓慢增加;继续提高烧结温度至1 020 ℃,由于烧结温度、烧结压力及由二者引起的塑性变形作用使材料密度升高,同时,随烧结温度的升高,奥氏体均匀化程度提高,组织中生成了片间距不等、数量更多的珠光体,提高了材料的硬度及强度.     

烧结温度对粉末冶金304不锈钢组织和性能的影响北大核心

采用真空烧结制备了304奥氏体粉末冶金不锈钢,研究了不同烧结温度对粉末冶金304不锈钢材料显微组织、密度、抗拉强度和耐腐蚀性能的影响。结果表明:随着烧结温度由1210℃升高到1300℃,304不锈钢烧结体组织孔隙数量减少、孔隙尺寸明显减小,当烧结温度提高到1360℃时,烧结体组织中晶粒逐渐长大并粗化,孔隙尺寸增大。随着烧结温度升高,烧结体的密度、硬度、抗拉强度和耐腐蚀性能先增大后减小。最佳烧结温度为1300℃,此时烧结试样具有最大的密度、硬度和抗拉强度,分别为7.23 g/cm^(3)、HRB68.88、344.19 MPa,试样的自腐蚀电流最小,具有最佳的耐腐性能。     

Cr,Mn,Co,Ni替代对LaFe11.5Si1.5磁性与磁热效应的影响

通过X射线衍射和磁性测量手段研究了由Cr,Mn,Co,Ni原子替代LaFe11.5Si1.5化合物中的Fe原子,对化合物结构、磁性与磁热效应的影响.结果表明:替代后的所有化合物的主相均为NaZn13型立方结构并存在杂相,衍射数据精修图表明杂相分别为1.3％的α-Fe相和2.5％的LaFeSi相.Cr,Mn和Ni的替代Fe使LaFe11.5 Si1.5化合物的居里温度与饱和磁化强度下降,而Co的替代化合物的居里温度与饱和磁化强度且增加.所有的替代均使化合物的热滞下降.对Cr,Mn,Fe,Co,Ni替代Fe的化合物在0～5.0T的磁场下最大磁熵变-△Sm分别为23.8,19.8,26.4,20.0和25.9 J·(kg·K)-1.     

磁温度补偿合金对永磁体补偿效果的表征

采用外补偿法改善Nd-Fe-B永磁材料的磁性能温度稳定性。讨论了磁温度补偿合金与永磁体组合后的磁性能和温度稳定性的表征。研究表明:用组合磁体的最大磁能积可以表征其磁性能,用开路法测试的可逆磁通温度系数可表征组合磁体的磁性能温度稳定性。用本实验室开发的磁温度补偿合金得到的组合磁体的可逆磁通温度系数小于0.001%/℃(20~100℃),室温下的最大磁能级达到195 kJ.m-3。外补偿法不仅能够有效地改善Nd-Fe-B永磁材料的磁性能温度稳定性,而且能够保持较高的磁性能。     

烧结温度对钴基耐磨合金微观组织和性能的影响

在真空环境下采用粉末冶金法制备碳化物增强钴基耐磨合金,利用扫描电子显微镜(scanning electron microscope,SEM)、电子探针显微分析仪(electron probe microanalyzer,EPMA)、X射线衍射仪(X-ray diffractometer,XRD)等设备观察和分析烧结温度对合金微观组织的影响,研究了增强相的物相及其形成机制。研究结果表明:粉末冶金法制备的钴基耐磨合金基体由面心立方(face center cubic,FCC)结构的γ-Co和密排六方(hexagonal closed-packed,HCP)结构的ε-Co相组成,增强相为M6C和M_(23)C_6型碳化物。当固相烧结温度为1250℃时,块状M6C型碳化物和颗粒状M_(23)C_6型碳化物弥散分布于基体中;当烧结温度升高至1340℃,M6C型碳化物呈尖锐的棱角状,平均尺寸大于30μm,颗粒状M_(23)C_6消失;烧结温度继续升高至1360℃,M6C型碳化物呈骨架状,ε-Co相消失。对合金的力学性能测试结果表明,当烧结温度为1270℃时,钴基合金的综合性能最佳,硬度大于HRC 60,抗压强度为1921 MPa,抗拉强度为203 MPa,摩擦系数为0.561。     

加入纳米Ni粉对微米级Fe粉试样烧结工艺及性能的影响

进行了真空状态下微米级Fe粉试样以及加入纳米Ni粉的微米级Fe粉试样的烧结试验。得出如下结论:添加1%纳米Ni粉的微米级Fe粉试样在900℃真空烧结2h的烧结体强度(289.61MPa)比微米级铁粉试样的烧结体强度(255.47MPa)提高13.4%。在保持烧结性能不降低的前提下,添加1%纳米Ni粉可使微米级Fe粉的烧结温度降低100℃或烧结时间缩短1h。     

烧结温度对高矫顽力Sm2(Co,Fe,Cu,Zr)17永磁体磁性能的影响

为深入了解高矫顽力Sm2(Co,Fe,Cu,Zr)17永磁体烧结温度与磁体磁性能的关系，设计了6种不同烧结温度，分别测试了各温度下烧结试样的密度和磁性能。试验结果表明：高矫顽力Sm2(Co,Fe,Cu,Zr)17磁体的密度随着烧结温度的升高而升高，在1210－1220℃达到最大值；磁体在1205－1210℃烧结时有较高的磁性能，内禀矫顽力超过1910kA/m，最大磁能积达到210kJ/m^3，温度过高或过低都使磁本性能下降；剩磁Br随磁体密度的升高而上升，矫顽力Hci的变化是密度和晶粒大小及胞状尺寸综合作用的结果。     

La_(1.1)Fe_(11.4)Si_(1.55)Ge_(0.05)合金的磁热效应

使用电弧熔炼法制备了La1.1Fe11.4Si1.55Ge0.05合金。研究了用少量的Ge替代Si后,La1.1Fe11.4Si1.55Ge0.05合金的磁性和磁热效应。粉末X射线衍射结果表明:在1273K真空退火处理10d后,合金La1.1Fe11.4Si1.55Ge0.05主相为NaZn13型立方结构,存在微量的α-Fe相。热磁曲线M-T与Arrott曲线表明:在居里温度Tc=205K处发生由铁磁性(TTc)转变为顺磁性(TTc)的二级磁相变。在磁场变化0～1.5T下,根据等温磁化曲线通过Maxwell关系式计算得出最大磁熵变-ΔSmmax=9J.kg-.1K-1。Ge替代Si后该合金在其居里温度Tc处-ΔSm-T曲线半高宽增大,使合金的相对制冷能力RCP(S)有所提高。     

烧结温度对利用废钢粉制备铁基粉末冶金制品的影响

以废钢粉取代普通钢粉制备铁基粉末冶金制品可以大幅度降低生产成本,节约资源。通过测定其密度、硬度与弯曲强度,重点研究了烧结温度对铁基粉末冶金制品性能的影响。结果表明,当温度不超过1180℃时,试样的密度、硬度随着烧结温度的上升而逐渐增加。试验最佳烧结温度为1170℃,此时试样的弯曲强度达到最大值724.15M Pa,随着温度的继续升高,弯曲强度下降。     

热等静压铁钴镍基高温合金的显微组织和力学性能

以气雾化（gas atomization,GA）粉末为原料,采用热等静压（hot isostatic pressing,HIP）致密化烧结工艺制备Fe18Ni23Co25Cr21Mo8WNbC2铁钴镍基高温合金,研究热等静压温度对致密化Fe18Ni23Co25Cr21Mo8WNbC2粉末高温合金金相组织、力学性能和断口形貌的影响。结果表明:热等静压技术制备的高温合金致密化程度很高,烧结体由（Fe,Ni）固溶体相和弥散分布的M6C碳化物强化相组成;热等静压温度为950~1050 ℃时,烧结体的密度、力学性能随着热等静压烧结温度的提高而提高;当热等静压温度达到1100 ℃时,致密化烧结体晶粒组织明显长大,其力学拉伸性能降低;致密化烧结体的室温拉伸断口以穿晶断裂为主,局部区域晶粒被拉伸开裂,650 ℃高温断口为穿晶断裂和沿晶断裂的混合形貌,基体相存在沿应力方向被拉长的韧窝。     

Reexamination of tympanic membrane temperature as a core temperature

Controversies surrounding tympanic temperature (Tty) itself and techniques for measuring it have dampened the potential usefulness of Tty in determining core temperature (operationally defined here as the body temperature taken at a deep body site). The present study was designed to address the following questions. 1) Can a tympanic membrane probe be made that is safer and more reliable than its predecessors? 2) Why is the effect of facial cooling and heating on Tty so inconsistent in reports from different laboratories? 3) Is Tty still useful as a measure of core temperature? Data from this study, obtained with a modified thermocouple probe, suggest that the widely reported facial skin cooling effect on Tty is most probably due to thermal contamination from the surrounding ear canal wall and/or suboptimal contact of the probe sensor with the tympanic membrane because 1) Tty that fell during facial cooling was increased to the precooling level by the repositioning of the probe sensor; 2) Tty determined by using a probe with a larger sensor area (the sensor soldered to a steel wire ring)tended to fall in response to facial cooling, whereas Tty determined with a thermally insulated probe ring did not; and 3) Tty obtained under careful positioning of the insulated probe was relatively insensitive to facial cooling or heating. Because Tty was practically identical to esophageal temperature (Tes) in the steady state, i.e., 36.83 +/- 0.20 (SD) degrees C for Tty and 36.87 +/- 0.16 degrees C for Tes at room temperature (n = 11), and because facial cooling had little effect on both Tty and Tes (36.86 +/- 0.17 degrees C for Tty and 36.86 +/- 0.26 degrees C for Tes during facial or scalp skin cooling), we support the postulate that Tty is a good measure of core temperature. The temperature transient in response to foot warming was detected 5 min (n = 2) faster with Tty than with Tes. Thus, with further improvements in the design of the probe. Tty can become a standard for determination of core body temperature.     

Disorders of temperature regulation

A remarkably effective and efficient thermoregulatory apparatus enables humans to maintain a normal body temperature despite widely varying and changing environmental and internal thermal conditions. Nevertheless, extreme ambient cold or heat and exhaustive exercise stress can overwhelm these defenses, leading to dangerous hypothermia or hyperthermia, respectively.     

红外测温技术在高温液体连续测温系统中的应用

将红外测温技术和光纤传导技术引入高温液体连续测温系统,实现连铸中间包钢水温度的连续测量,克服了热电偶存在的间断测量、需要经常更换等缺陷,和国内外同类产品相比,具有响应速度快、连续测温时间长、测量成本低、精度高等优点。简要介绍红外测温理论、实用测温数学模型的建立与应用、连续测温系统的组成及其测量原理。     

The effects of austenitization temperature on the high temperature ductility of Fe-P-S Alloys

The tensile ductility of high purity iron, containing 20 wt ppm S and 40 to 280 wt ppm P, was measured at 700 °C after austenitization at various temperatures. All samples were cooled from the austenitization temperature and reheated to the test temperature in the same way. The shape of the ductility (as measured by percent reduction of area at fracture) vs austenitization temperature curve was found to depend strongly on phosphorus levels: For 40 wt ppm P a deep ductility minimum, caused by grain boundary cavitation and intergranular failure, was found after austenitizing at 1100 °C; for 180 wt ppm P a less pronounced minimum was found; but for 220 and 280 wt ppm P the minimum disappeared completely and the samples showed 95 pct or greater ductility and necked almost to a point. It is proposed that the low ductilities and intergranular failure in the low P samples are caused by the segregation of S to oxide-ferrite interfaces in the grain boundaries, resulting in a weakened interface and easy cavity nucleation. The cavitation decreases for austenitization treatments above 1100 °C because of desorption of S from the boundaries. No mechanism is proposed for austenitization temperatures below 1100 °C. It is suggested that P additions improve the ductility by competing with S for sites on the oxide-ferrite interface, thereby reducing the amount of segregated S. This paper is based on a presentation made in the symposium “Crack Propagation under Creep and Creep-Fatigue” presented at the TMS/AIME fall meeting in Orlando, FL, in October 1986, under the auspices of the ASM Flow and Fracture Committee.     

IF钢加热和连退温度对成品质量影响分析

以深冲钢 DC06 为研究对象,在实验室条件下,模拟分析了不同连铸坯加热温度(1 150～1 250 ℃)和不同连退温度(760～840 ℃)工艺组合下 IF 钢连退成品的微观组织、析出物和力学性能。结果表明,降低连铸坯加热温度可以粗化连退成品的晶粒和析出物,提高连退成品的应变硬化指数和断后伸长率,并降低连退成品的强度。在连退成品性能要求一定的情况下,可以配以更低的连退温度,从而实现降本增效。