Effects of External Stresses on the Carbide Precipitation in Bainite Transformation

TEM observation of carbide precipitates in bainite has been carried out for steel 40CMD8. Specimens transformed at 350℃ and 450℃ without external stress contain respectively the lower and the upper bainite. No fundamental change in carbide precipitation is observed in specimen transformed at 350℃ under stress of 128MPa. The very fine cementite is found precipitated within the upper bainite plates in specimen transformed at 450℃ under stress of 144MPa, which can be explained as the result of the difficulty of carbon diffusing out of the massive ferrite plate within a much shortened transformation time due to the external stress. For all the specimens examined, Bagaryatskii orientation relationship is found existing between the carbides and ferrite matrix.     

控轧控冷和回火工艺对超低碳贝氏体钢组织和性能的影响

研究超低碳贝氏体钢的控轧控冷和回火工艺对其组织及力学性能的影响。结果表明,在试验工艺下试样组织均为粒状贝氏体,且在820℃终轧、440℃回火时获得了高强度低屈强比的超低碳贝氏体钢;控轧控冷工艺可以细化贝氏体铁素体和M-A岛、降低铁素体含碳量、控制组织中软硬相的比例,从而提高材料强度、降低其屈强比。回火温度升高使贝氏体铁素体粗化、含碳量和位错密度降低、M-A岛分解成细小的板条贝氏体,并析出富铜原子团,这是材料获得高强度、低屈强比的主导因素。     

Influence of isothermal bainitic processing on the mechanical properties and microstructure characterization of TRIP steel

The mechanical properties of transformation induced plasticity (TRIP) steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM, SEM, XRD and TEM. The volume fraction of retained anstenite and the carbon content in anstenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained anstenite was analyzed by the volume fraction of retained austenite and the carbon content in retained anstenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite. To obtain good mechanical properties, the optimal conditions of isothermal bainitic tem-perature and holding time are 410-430℃ and 180-240 s, respectively. After isothermal bainitic processing under the optimal condi-tions, the corresponding volume fraction of retained anstenite is 5vol%-15vol%, which can provide enough retained austenite and plastic stability for austenite with high carbon content.     

Electromigration in eutectic SnAg solder reaction couples with various ambient temperatures and current densities

The electromigration behavior of eutectic SnAg solder reaction couples was studied at various temperature (25 and 120℃)when the current density was held constant at 10~4 A/cm~2 or 5×10~3 A/cm~2. Under the current density of 10~4 A/cm~2, scallop type Cu_6Sn_5 spalls and migrates towards the direction of electron flow at room ambient temperature (25℃), but transforms to layer type Cu_3Sn and leaves Kirkendall voids in it at high ambient temperature (120℃). Under the current density of 5×10~3 A/cm~2 plus room ambient temperature,no obvious directional migration of metal atoms/ions is found. Instead, the thermal stress induced by mismatch of dissimilar materials causes the formation of superficial valley at both interfaces. However, when the ambient temperature increases to 120℃, the mobility of metal atoms/ions is enhanced, and then the grains rotate due to the anisotropic property of metal atoms/ions is enhanced, and then the grains due to the anisotropic property of β-Sn.     

气控钠热管炉热特性实验研究

为探索气控热管在计量领域的应用,研究气控钠热管炉热特性.在未控压的状态下,找出加热炉最佳控温点,研究气控钠热管在同一温度计阱不同位置上和不同温度计阱中的温度稳定性和温度场均匀性,对加热炉丝2种不同的绕制方式进行讨论.实验结果表明,将热管内温度控制在655℃、气路压力控制在7.840 kPa的状态下,热管温度稳定性在15 min内达到±0.836 4 mK.     

热穿-热轧法生产的新型贝氏体中空渗碳钢的组织和性能

用热穿-热轧法制备了新型贝氏体中空钢．研究了热处理对新型贝氏体钢和渗碳处理对中空钢组织和性能的影响．结果表明：新型贝氏体钢正火＋低温回火热处理后的组织为贝氏体铁素体和奥氏体,淬火＋低温回火后的组织由马氏体、贝氏体和奥氏体组成;正火或淬火＋低温回火后,新型贝氏体中空钢具有良好的强韧性．正火＋低温回火后,中空钢的组织为贝氏体铁素体和残余奥氏体组织．新型贝氏体中空钢渗碳后空冷,渗层的组织为高碳马氏体和残余奥氏体组织,非渗层为贝氏体铁素体和残余奥氏体组织,实体中空钢具有较好的强韧性和渗碳效果．     

基于ANSYS的场发射阵列阴极焊接应力研究

该文基于ANSYS平台模拟了场发射阵列阴极与钼电极钎焊工艺参数对钎焊层等效应力的影响,并根据仿真结果进行了实验验证。仿真结果表明,当钎焊温度为850 ℃时,最大等效应力最小;当降温速率为23 ℃/min时,最大等效应力最大,之后随降温速度的增加而迅速减小;在降温过程中,高温区逐渐向硅基底扩展,温度沿焊缝方向呈对称分布,焊缝中心温度高,两边温度低。测试结果表明,钎焊接头组织致密,焊缝结合良好,没有裂纹和空洞等缺陷,且钎料对硅基底的影响很小。这是一种可行的、低成本的实现硅基场发射阵列阴极焊接的有效方法。     

三七提取中人参皂苷的转化

为提高三七自身含有的人参皂苷糖苷酶的作用,采用TLC和HPLC方法检测,研究了不同温度水提三七过程中人参皂苷的变化。结果表明,在80~100℃,15%以上三七中的人参皂苷Rb1、Rd、Re、Rg1转化为Rg2、Rg3、Rh2、C-K等稀有人参皂苷;提高温度到110~121℃时完全转化;而人参皂苷本身对温度很稳定,在80~121℃不发生转化。这说明三七提取中人参皂苷的变化,主要不是温度的作用,而可能是自身酶等三七内部的特殊物质起的作用。     

树叶状Co和Co3O4的水热合成与磁性研究

以氯化钴（CoCl2·6H2O）和氢氧化钠作为反应前驱物,采用水热法合成微米级树叶状钴单质,在500℃退火条件下得到形貌相似的Co3O4粒子,并运用XRD、SEM和VSM对所得粒子的结构、形貌和磁性能进行了初步研究。结果表明,树叶状钴单质表现出室温铁磁行为,具有较高的磁参数,其中饱和磁化强度为139．3emu／g、矫顽力为29．5kA／m。同时发现,在500℃×1h退火后的CosOa还出现极弱的铁磁性行为,可能是未完全氧化的Co单质所产生。     

基于ANSYS的碳纤维约束混凝土棱柱体热应力分析

碳纤维增强塑料（CFRP）加固修复混凝土结构技术在国内外迅速的发展起来,它有高强、轻质、耐腐蚀耐疲劳、施工便利、不增加构件尺寸等优点,因此,在混凝土加固工程中得到大量的应用。由于碳纤维与混凝土的线膨胀系数的不同,在温差的作用下,碳纤维加固混凝土结构中将产生温度应力。本文应用ANSYS软件分别对在降温温差30、40、50、60℃作用下的碳纤维加固混凝土棱柱体进行了温度应力分析。     

Relaxation of Deformed Austenite and Refinement of Bainite in a Nb-Containing Microalloyed Steel

By means of stress relaxation and strain-induced precipitation in deformed austenite, bainite with micron sheaves size was ob-tained in Nb-containing steel. Microstructures of deformed samples isothermally relaxed for various time followed by cooling in water were examined. Stress relaxation test and transmission electron microscopy (TEM) were employed to detect precipitation of microalloy elements, such as Nb, Ti, during isothermal holding after deformation. All the samples were constituted by lath-like bainite along with acicular ferrite, but the size of bainitic sheaves and the amount of acicular ferrite were changed with relaxation time. To achieve optimum refinement, relaxation should be confined in the stage when the precipitates have sufficiently grown and started to coarsen. The sample having not undergone relaxation does not exhibit obvious refinement despite of its higher dislocation density. These results indicate that relaxation promotes bainite to refine, which is because deformed austenitic grains are divided by dislocation walls formed during rela-xation and acicular ferrite formed before bainitic transformation.     

纳米晶钇稳定氧化锆的制备及表征

以草酸盐为沉淀剂,通过化学共沉淀-高温煅烧法制备了系列钇稳定氧化锆,采用XRD分析技术对样品进行表征。结果表明,不进行钇掺杂时,ZrO2在煅烧温度较低时,晶型以t-ZrO2为主,煅烧温度提高,t-ZrO2向m-ZrO2转变,900℃时晶型已完全转变为m-ZrO2。掺杂钇后低温煅烧产物晶型为四方相,当掺杂钇的含量低于6%(摩尔分数)时,随着煅烧温度提高,少部分四方相转变为单斜相,转变比例随着掺杂量的提高而降低;掺杂钇的含量达到6%(摩尔分数)时,低温煅烧产物的晶型为四方相,随着煅烧温度的提高,晶型保持稳定。Y3+取代Zr4+产生氧缺陷是ZrO2晶体结构稳定化的主要因素。通过该方法制备的钇稳定氧化锆均为纳米晶,晶粒尺寸随着煅烧温度的提高而长大。     

高温脱胶提取棉秆皮纤维工艺

为解决棉秆皮纤维手感硬、纤维分离度差等问题,对棉秆皮纤维的高温脱胶方法进行了研究。先通过预氧处理,再进行高温脱胶制备棉秆皮纤维,采用正交试验研究了影响脱胶效果的主要因素,如氢氧化钠的质量分数、温度、保温时间和浴比对纤维木质素含量和残胶率的影响,并结合正交试验结果采用二次正交回归分析进一步优化脱胶工艺条件,确定最佳处理工艺为:氢氧化钠的质量分数11.26%,温度132.4℃,保温时间50min,浴比1∶20。对处理前后纤维的纵向结构进行扫描电镜分析,高温脱胶后纤维分离度得到很大提高。     

Dissolving of Nb and Ti carbonitride precipitates in microalloyed steels

The dissolving behaviour of Nb and Ti carbonitride precipitates in microalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electron microscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates in Nb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Ti in precipitates decrease gradually. These precipitates still existe even after holding for 48 h at 1300℃while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the same temperature. These results show that formation and thermostability of precipitates are considerably influenced by interaction between Nb and Ti.     

Dynamic observation of bainite transformation in a Fe-C-Mn-Si superbainite steel

The dynamic observations of bainitic transformation in a Fe-C-Mn-Si superbainite steel were conducted on a high temperature laser scanning confocal microscope. It is indicated that the mutual intersection of bainite sheaves often occurs during growth of bainite ferrite, resulting in an interlocked bainite microstructure. Moreover, bainite transformation is promoted by higher austenization temperature and the longer and finer bainite platelets are obtained. Further, The average growth rate of bainite after austenization at 1 100 ° is calculated as 5.8 µm·s^?1. In situ observation investigation makes it possible to identify bainite transformation in real time during isothermal holding.     

Medium-range order clusters in metal melts

Structures of molten metals Cu and Al, alloys Cu-Al, Al-Ni, Al-Fe and, Al-Si were investigated by using high temperature X-ray diffractometer. It has been found that there are not only short-range order structures (SRO) but also medium range order structures (MRO) in Cu-Al, Al-Ni, Al-Fe alloy melts. There are only short-range order structures in the pure metals Cu and Al and Al-Si alloy melts at different temperatures. It has also been found that the presence and the disappearance of the MRO structures in molten metals are a function of temperature. Moreover, the pre-peak in the structure factor is an indication of MRO in molten metals. There is a pre-peak in each structure factor S( Q) of Al-Fe alloy melt containing 14 wt% Fe, 16 wt% Fe and 19 wt% Fe at 1550℃, showing that there are the medium range order structures in these alloy melts. For Al-35wt% Ni alloy, the pre-peak exists in S(Q) when the temperature is lower than 1300?, and it is weakened drastically when the temperature surpasses 1300℃. The     

导热硅胶/相变材料复合组件在电池热管理中的应用

一种低温导热硅胶/相变材料复合组件在电池模组中的使用,有效地解决了相变材料由于液化而发生的析出问题,同时保持相变材料高导热与高潜热值.由于导热硅胶片具有一定的弹性与黏性,使得整个系统具有一定缓冲作用,减少了相变材料与电池之间的接触热阻,进一步提高了整个系统的散热性能.在3C放电倍率下,相比自然冷却方式的66.63 ℃,...     

Development of grain boundary allotriomorphic ferrite/granular bainite duplex steel

A new hot-rolled low alloy high strength steel with grain boundary allotriomorphic ferrite/granular bainite duplex micro-structure has been developed through novel microstructure and alloying designs without any noble metal elements such as nickel and molybdenum. Its as-rolled microstructure and mechanical properties, fatigue crack propagation behavior compared with single granular bainitic steel as well as continuous cooling transformation, were investigated in detail. The measured result of CCT (continuous cooling transformation) curve shows that such duplex microstructure can be easily obtained within a wide air-cooling rate range. More importantly, this duplex microstructure has much better combination of toughness and strength than the single granular bainite microstructure. It is found that the grain boundary allotriomorphic ferrite in this duplex microstructure can blunt the rni-crocrack tip, cause fatigue crack propagation route branching and curving, and thus it increases the resistance to fati     

高温水冷后循环加卸载条件下花岗岩的渗透性

针对水下隧道火灾喷水灭火降温过程中围岩的渗透性问题,对高温水冷后循环加卸载条件下花岗岩的渗透性开展了试验研究.以高温(25、400和900 ℃)水冷后的花岗岩试样为研究对象,通过轴向压应力循环加卸载过程中气体渗透性试验,研究花岗岩渗透率变化规律.结果表明:轴向压应力循环加卸载试验过程中,花岗岩试样的卸载模量随着高温水冷处理温度升高而减小,随着轴向压应力增大,卸载模量总体呈上升趋势,气体渗透率随温度升高而增大;花岗岩BET比表面积与BJH孔体积在900 ℃高温水冷后明显减小.     

轧制对AZ31/AZ91焊接接头组织及扩散的影响

为了理解异种镁合金焊接接头显微组织的变化规律,采用TIG焊接方法制备了AZ31/AZ91焊接接头,研究了轧制变形及热处理对AZ31/AZ91焊接接头显微组织及扩散系数的影响.结果表明,随着轧制变形量的增加,AZ31/AZ91熔合区的晶粒细化程度增大,但在随后的420℃×8 h固溶处理过程中,由于再结晶充分,因此晶粒逐渐变大.在420℃×2 h固溶处理过程中,Al的扩散系数随轧制变形量的增加而增大;在420℃×8 h固溶处理条件下,Al的扩散系数随轧制变形量的增加而减小.相同轧制变形量下,Al的扩散系数随着保温时间的增加而减小.