工业纯钛ECAP温变形的组织研究

采用两通道夹角为90°,外圆角为20°的模具,实现了工业纯钛BC方式6道次的ECAP温变形,累积等效真应变达到6.3,并观察分析了变形试样的显微组织.结果表明:工业纯钛经BC方式6道次ECAP温变形后,获得了晶粒尺寸为150 rm的具有大角度晶界的超细晶组织;工业纯钛在ECAP温变形过程中,随变形道次的增加,通过位错滑移产生的板条和不稳定的孪晶组织相互作用,大量的位错聚积成位错胞并生成亚晶;在变形温度的影响下,位错相互作用,使亚晶逐渐演变成具有大角度晶界的超细晶组织.     

等通道挤压镁合金工艺的研究

采用等通道挤压(ECAP)对AZ91镁合金在预热温度为350、400、450、500 ℃下进行了2、4、6、8、10道次的挤压.采用光学显微镜和透射电子显微镜分析了试样经过不同的变形工艺的显微组织变化.结果表明,随着挤压道次和变形温度的增加,ECAP变形后的试样表面形态愈加平滑光洁,晶粒可细化到几微米,在透射电镜下观察ECAP后的显微组织,晶粒内部出现高密度位错,产生位错塞积.第二相粒子阻碍位错运动,从而促进动态再结晶,对细化晶粒起着重要作用.     

超低温等通道转角挤压高导电单晶铜的霍尔佩奇强化

分别采用光学显微镜、扫描电镜、X射线衍射仪和电子背散射衍射分析超低温等通道转角挤压(ECAP)中等应变量单晶铜的形变组织和织构演变，测试材料的力学和导电性能，分析材料组织转变机理及其对材料力学和导电性能的影响。结果表明，超低温ECAP早期形成的定向剪切带在后续变形过程中会严重影响材料组织的转变过程。增加应变量，A路径变形中剪切带内部会形成高密度的位错塞积，特征晶界占比增加；B_C路径变形时剪切带内部的位错发生强烈的交互作用；C路径变形后剪切带的取向发生分散。经过6道次变形后，单晶铜组织中形成强烈的{111}<112>织构，材料强度从初始126.0 MPa增加到400.2 MPa，而导电率仍保持在98%IACS以上。低温ECAP变形后组织内部形成定向剪切带并产生高密度的位错，位错间相互缠结，有效阻碍了位错滑移，而晶粒仍保持良好的单晶特性。     

双相合金Mg-8Li-1Al的等通道转角挤压Ⅱ.挤压后合金的室温拉伸性能

随着等通道转角挤压(ECAP)次数的增加，Mg-8Li-1Al(质量分数，％)合金的室温拉伸强度和塑性同时增加，对应1，2，3，4次ECAP，合金的屈服强度分别为169，185，196和198MPa，延伸率分别为12％，14％，25％和27％，微观组织分析表明，ECAP方法在细化两相组织、提高合金强度的同时，还改善了α相组织的均匀性和等轴性，并使各晶粒间的取向差逐渐增大，这种处在非平衡状态的、具有较大取向差的晶界结构，在室温拉伸变形过程中可激活晶界滑移或晶粒转动等变形方式，进而使材料的塑性随道次增加而得到提高。     

剪切模式下Ti-1300合金组织及织构演变规律

通过光学显微镜(OM)、透射电子显微镜(TEM)、X射线衍射(XRD)等检测方法,研究等通道转角挤压变形后Ti-1300合金的组织与性能。研究结果表明:Ti-1300合金经过ECAP变形,发生晶粒转动、晶内多系滑移以及晶界处螺型位错与刃型位错的混合位错交错排列的协调作用,致使晶界不能破碎,原始晶界清晰可见,晶内出现大量的相互交错的剪切滑移带,显微组织中存在大量平行细密的板条组织以及位错团、位错胞,位错密度增大,但在整个ECAP变形过程中并未产生形变诱导ω或α″相。织构分析结果表明ECAP变形过程中Ti-1300合金初始(110)■织构逐渐转变为α织构,并形成D织构及立方织构。     

等通道挤压镁合金的微观组织与硬度

对ZK60镁合金进行了C方式(相邻道次间旋转180°)等通道角挤压.采用光学显微镜、扫描电子显微镜和透射电子显微镜分析了试样ECAP变形前后的显微组织变化;采用显维维氏硬度计进行了硬度测试,并分析了ECAP变形对材料硬度的影响规律.结果表明:在ECAP挤压后的组织中有高密度的位错,它促成再结晶并晶粒细化到1～3μm;在经过6道次挤压后,合金的硬度达到76.3 HV.     

等通道转角挤压对Mg-6Zn合金显微组织和力学性能的影响

利用等通道转角挤压(ECAP)技术,在200℃对Mg-6Zn合金进行了不同道次的挤压。结果表明,经ECAP挤压后合金显微组织明显细化、均匀化,平均晶粒尺寸由15μm减小到3μm;ECAP过程中粗大的块状共晶相变形破碎、细化,并在周围诱发新相析出。通过XRD分析发现析出相主要是Mg_4Zn_7和MgZn_2。经过2道次ECAP挤压后,Mg-6Zn合金的抗拉强度可达275 MPa,屈服强度达到245 MPa,伸长率为24%。当ECAP道次增加到4道次和6道次后,强度反而下降。     

等通道转角挤压过程中纯铜位错密度变化和力学性能

利用等通道转角法(Equal channel angular pressing)对纯铜进行挤压变形,研究变形过程中纯铜组织演变,分析位错密度及其相应力学性能变化规律,探讨层错能对组织演变的影响机理。结果表明:退火后纯铜在ECAP变形过程中由小角度晶界逐渐转变为大角度晶界,晶粒尺寸细化到5~10μm;随着挤压道次的增加,纯铜中位错密度显著增大,1道次时位错密度为0.16×1014 m-2,6道次后位错密度达到最大值,为0.41×1014 m-2,之后位错重组和湮灭使得位错密度在一定程度上减小;材料强度明显提高,塑性减小,退火后纯铜的抗拉强度为220 MPa,伸长率为53.5%,8道次后纯铜的抗拉强度为444 MPa,伸长率下降到22.1%;纯铜拉伸断口韧窝数量逐渐增多、变浅且分布均匀,断裂方式整体表现为塑性断裂。通过对组织演化和力学性能分析得出,纯铜作为中等层错能材料,同时具有低层错能和高层错能金属的一些变形特征。     

等通道角挤压AZ31镁合金的微观组织与力学性能

借助X射线衍射仪、光学显微镜等分析设备,研究了AZ31镁合金在等通道角挤压变形过程中微观组织与力学性能随加工道次的变化行为.结果表明,随挤压道次的增加,晶粒不断细化,力学性能发生显著变化,伸长率不断增大,抗拉强度逐渐降低.挤压8道次后,晶粒尺寸由最初的120μm减小到9μm.由于晶粒细化效应,导致α相主要变形机制由1道次的孪生变为随后道次的位错滑移.挤压后(0001)晶面的取向分布分散性,影响抗拉强度.伸长率的增大与晶粒细化和滑移面的激活有关.     

NiTiNb合金等径角挤压时的变形行为及微观组织演变规律研究

研究了等径角挤压(ECAP)对NiTiNb合金的变形行为和微观组织演变规律,并分析了挤压道次对组织的影响。结果表明,挤压过程中载荷先增大后迅速降低,4道次变形后,(Ti,Nb)2Ni硬脆相完全消失。此外,TiNi基体相经ECAP变形后明显细化。     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.