连铸速度对CuAlNi记忆合金晶粒长大及弯曲疲劳的影响

以4种速度连铸了柱状晶组织的CuAlNi记忆合金丝并热处理，检验其晶粒长大及弯曲疲劳性能。连铸速度大于240mm／min，72相的析出被抑制；速度达480mm／min时由于凝固前沿液相受到激冷而形成等轴晶。360mm／min为柱状晶加热长大的临界连铸速度。超过此速度，加热时晶粒将急剧长大。临界连铸速度以下提高连铸速度可细化晶粒，经热处理消除内应力后，弯曲疲劳断裂次数可大幅提高。     

热型连铸超弹性CuAlNi合金丝的拉伸疲劳性能

用热型连铸法以不同速度连铸了φ1.5的柱晶CuAlNi合金丝,研究其拉伸疲劳性能.结果显示：铸态下,连铸速度由240mm/min提高到360mm/min时合金丝由于晶粒细化提高了疲劳寿命;铸态下少量γ2对拉伸疲劳没有显著影响;疲劳拉伸中柱晶晶界开裂,阻隔了疲劳裂纹扩展,降低了疲劳裂纹对表面缺陷的敏感性,有利于提高疲劳寿命.     

热型连铸铝线的制备及其显微组织和性能

采用自制的热型连铸设备制备铝线材料,研究铸型温度和拉铸速度等工艺参数对材料表面质量、显微组织及力学性能的影响,通过对最佳工艺条件下制备的铸锭断口形貌进行观察和分析,探讨其相关机理。结果表明:当铸型温度为675~685℃、拉铸速度为90~120 mm/min时,可以制备出表面质量较佳的铸锭;同时,工艺参数会对晶体的择优取向产生一定影响,当铸型温度和拉铸速度分别为680℃和90 mm/min时,晶体的取向更倾向于沿?100?方向生长,铸型温度越高,铸锭力学性能越优异。当拉铸速度为90 mm/min时,制备的热型连铸铝线具有最佳的塑性加工能力。相比于普通多晶铝线,热型连铸铝线具有更好的塑性。     

制备参数对HCCM水平连铸纯铜板坯组织与力学性能的影响

采用热冷组合铸型(HCCM)水平连铸制备横断面尺寸70 mm×10 mm(宽度×厚度)具有强轴向取向柱状晶组织的纯铜板坯,研究工艺参数对纯铜板坯微观组织、表面质量与力学性能的影响。结果表明:在铜液铸造温度1250℃,热型段温度1100~1150℃,冷却水流量600 L/h、连铸拉坯速度20~80 mm/min条件下可以制备出表面粗糙度低、具有沿拉坯方向强取向组织和优良力学性能的纯铜板坯,其抗拉强度为137~141 MPa,断后伸长率为45.1%~61.7%。随着拉坯速度的增加,HCCM水平连铸所制备纯铜板坯的组织均匀性增加,晶粒尺寸变小;热型段温度升高时板坯的柱状晶组织的晶界更加平直;而总体上力学性能受拉坯速度和热型段温度的影响较小。采用HCCM水平连铸,在热型温度为1150℃时制备的纯铜板坯的表面粗糙度小于0.3μm,无需进行铣面可直接进行后续冷加工,可为发展铜板带短流程生产工艺奠定基础。     

热型连铸超弹性CuAlNi合金丝的拉伸疲劳性能

用热型连铸法以不同速度连铸了φ1．5的柱晶CuAlNi合金丝,研究其拉伸疲劳性能。结果显示:铸态下,连铸速度由240mm／min提高到360mm／min时合金丝由于晶粒细化提高了疲劳寿命;铸态下少量γ2对拉伸疲劳没有显著影响;疲劳拉伸中柱晶晶界开裂,阻隔了疲劳裂纹扩展,降低了疲劳裂纹对表面缺陷的敏感性,有利于提高疲劳寿命。     

真空熔炼氩气保护下连续定向凝固铜管的制备技术

采用自行研制的真空熔炼、氩气保护连续定向凝固设备制备出具有连续柱状品组织的铜管铸坯,分析了铜管铸坯生产中熔体温度、连铸速度、冷却水量,结晶器等对其的影响.分析了在连续定向凝固过程中组织的淘汰机制.实验结果显示,合理参数范围分别为熔体温度1 130～1 170℃、牵引速度20.8～70.0mm/min、冷却水量800～1 000L/h、真空度6.6～20Pa.     

热型连铸设备与工艺的研究现状

首先回顾热型连铸法的发展历程以及连铸装置的3种不同拉铸方式,介绍了设备系统的组成及其作用。着重从稳定的定向凝固组织形成条件及温度场、铸型温度、拉铸速度、冷却条件和液面高度等工艺参数方面进行阐述并结合实例分析该工艺参数对铸锭质量的影响。最后为以后热型设备的进一步改进做出假设与设想。     

连铸工艺参数对高碳钢小方坯凝固组织的影响

通过CAFE模型,对SWRH82B钢小方坯的凝固组织进行数值模拟,研究了中间包钢水过热度、连铸坯拉速、二冷比水量对铸坯凝固组织的影响规律。结果表明,钢液过热度从5℃增加到45℃,铸坯的等轴晶率从39.7%不断减小到23.1%,晶粒尺寸变大;过热度为25~35℃时,等轴晶率和晶粒尺寸变化小。二冷比水量从0.5 L/kg增加到0.8 L/kg时,铸坯等轴晶率逐渐从34.4%减小到29.2%,但是晶粒尺寸不断变大。比水量达到0.8 L/kg后,继续增加将不再减小铸坯等轴晶率,但是会细化晶粒。拉速从1.25 m/min提高到2.25 m/min,铸坯等轴晶率由29.1%不断增大到38.3%,晶粒也随之不断细化。     

拉速对紫铜水平连铸坯凝固行为及组织场影响规律研究

水平连铸是生产铜板带坯的常用方法，探索工艺参数变化对铸坯质量的影响规律十分重要。采用数值模拟的方法分析了水平连铸拉速变化对结晶器内温度场、液穴深度、冷却速率等的影响规律，并结合工艺试验揭示了拉速变化对铸坯组织的影响机理。结果表明，随着铸坯拉速的不断提高，结晶器内的液穴深度持续增加，铸坯表面和芯部沿牵引方向的冷却速率均逐渐降低，且二者的冷却速率差值逐渐减小，当拉速为149 mm/min时，二者冷却速率达到相同；随着铸坯拉速的不断提高，铸坯截面上晶粒生长方向与牵引方向的夹角θ逐渐增大，晶粒生长距离缩短，铸坯表面上晶粒数目增加，平均晶粒直径从1.96 mm逐渐减小到1.05 mm，整体组织均匀性明显提高。     

热型连铸工艺的开发应用

热型连铸工艺可实现定向凝固,并且铸件与铸型间的摩擦力很小。本文介绍了用热型连铸工艺开发的单晶铜杆,用于高质量传输数字信号和模拟信号;柱晶组织的CuAlNi形状记忆合金丝,消除了铜基记忆合金的晶界应力集中,大大提高合金的力学性能和记忆性能;具有内肋片的铜管,提高换热效率3~5倍;连铸了塑性加工难度很大的白铜管坯,提高了塑性加工性能和耐海水腐蚀性能。     

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.     

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.     

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.     

RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE

To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.