Low-temperature processing of Fe–Al intermetallic coatings assisted by ball milling

A novel technique has been developed to produce Fe–Al intermetallic coatings on steel. This technique applies mechanical vibration to a retort, which is loaded with Al powder, alumina filler, ammonium chloride activator and FeCrAl alloy balls. The operation temperature was from 440 to 600 °C. This technique produced coatings with thickness of 17 μm for 15 min and 90 μm for 120 min treatment at 560 °C. The coatings appear to be homogeneous, with a high density and free of porosity, and have excellent adherence to the substrate. The coatings consisted mainly of η-Fe₂Al₅ with small amounts of θ-FeAl₃ and β-FeAl, and exhibited a nano-structure. Microstructure studies suggested that the formation of the intermetallic phases at a low temperature has a complex mechanism, including the formation of a thin Al layer on the substrate by ball milling; Al-rich phases nucleation, growth and formation of an initial alloy layer; severe plastic deformation which increases the local temperature and produces a nano-structure; and fast outward diffusion of Fe and formation of Fe–Al intermetallics. This technique reduced the treatment temperature and duration significantly compared with the conventional Al pack cementation processes, providing a new approach to industrial diffusion coatings with great energy and time savings.     

Effect of particle size on the surface oxidation and flotation behavior of galena particles in lime system

ABSTRACT

In this research, the effect of particle size on the surface oxidation and flotation behavior of galena in the lime system was studied. Coarse (?0.074 + 0.038 mm), intermediate (?0.038 + 0.025 mm) and fine (?0.025 mm) galena particles were used in the experiment. The dissolution tests, flotation tests, and sorption tests were accomplished. Through further analysis by XPS, the effect of particle size and lime was observed. The decrease of mineral particle sizes increased the adsorption ratio of collector and the dissolution of galena, while the hydrophilic product OH^?/Ca(OH)⁺ produced by dissolution occupied the dominant position, which led to the minerals hydrophilic.     

乘客等待条件下的电梯优化调度模型

对多部电梯进行综合调控管理具有广泛的现实意义,本文提出了在乘客等待条件下的电梯调度问题,以作为上班高峰期电梯优化调度的一种近似。并利用概率论的方法得到了电梯往返运行一次的平均时间,建立了电梯优化调度的数学模型,且采用动态规划的方法求得了乘客在等待条件下的最优调度方案,并对实例进行了计算。     

Determination of surface heat-transfer coefficients of steel cylinder with phase transformation during gas quenching with high pressures

In numerical simulation of quenching process, the boundary conditions of temperature field and stress field are very important, in which the boundary conditions of temperature field are very complicated. In order to simulate the thermal strains, thermal stresses, residual stresses and microstructure of the steel during gas quenching by means of the numerical method, it is necessary to obtain an accurate boundary condition of temperature field. The surface heat-transfer coefficient is a key parameter. The explicit finite difference method, non-linear estimate method and the experimental relation between temperature and time during quenching have been used to solve the inverse problem of heat conduction. The relationships between surface temperature and surface heat-transfer coefficient of cylinder have been given. The non-linear surface heat-transfer coefficients include the coupled effects between phase transformation and temperature. In calculation, physical properties were treated as the function of temperature and volume fraction of constituent. The results obtained have been shown that this technique can determine effectual the surface heat-transfer coefficients during gas quenching.     

Study on characteristics of Ni-W-B composites containing CeO2 nano-particles prepared by pulse electrodeposition

Ni-W-B composites containing CeO2 nano-particles on the surface of 45 steel were prepared by pulse electrodeposition,and the in-fluence of pulse frequency,pulse duty circle and heat treatment temperature on the structures and properties were investigated.The results in-dicated that the pulse co-deposition of Ni,W,B and CeO2 nano-particles led to Ni-W-B/CeO2 composites possessing higher microhardness and better wear resistance when heat-treated at 400 oC for 1 h.The microhardness of 636 HV and the deposition rate of 0.0281 mm/h of the as-deposited alloy were the highest at pulse frequency of 1000 Hz,pulse duty circle of 10% and pulse average current density of 10 A/dm2.The composites were mainly in the amorphous state and were partially crystallized as-deposited,and the crystallization trend was strength-ened when heat-treated at 400 oC.Decreasing pulse duty cycle from 75% to 10% was favorable to the refinement in grain structures and im-provement of microstructures.The crystal sizes of the composites were smaller by means of pulse electrodeposition.     

混凝土喷射机出料管防粘结措施研究

利用有限元分析软件ANSYS对湿式混凝土喷射机关键零件出料管进行了结构动力学分析,计算了出料管的固有频率及振型,通过对结果的分析提出了出料管防粘结方法和措施,对实际中解决出料管粘料问题具有一定的理论研究和参考价值.     

M23C6 precipitation and Si segregation promoted by deep cryogenic treatment aggravating pitting corrosion of supermartensitic stainless steel

The microstructure evolution and the pitting corrosion resistance of a supermartensitic stainless steel after deep cryogenic treatment process were clarified th...     

脉冲电流在改善金属凝固组织中的作用

综述了脉冲电流在改善金属凝固组织方面的研究现状。从理论上归纳和分析了脉冲电流在金属凝固过程中产生作用的主要机制。     

贵州某卡林型金矿石浮选优化试验研究

对贵州某卡林型金矿的浮选工艺进行了参数优化试验研究,得到了浮选最佳药剂条件,在不脱泥的情况下,最终金的回收率达91.64%,浮选金精矿品位为42.60g/t。     

Real-time emergency route generating algorithm in tunnel

As part of the digital mine system, a real time emergency route generating algorithm for a large scale metal mine is studied. The tunnel is abstracted and mathematically described by the center line model. A series of definitions are made and the center lines are regularized. In order to improve the quality of the final routes, a center line dataset preprocessing is done according to the factors including the slope threshold and the tunnel closed state information, etc. While in preprocessing, the mineshaft and shaft with the steep slope are excluded implicitly. The interface is preserved for point-like objects (e.g. blowers), directions (e.g. wind direction of blowers) and so on. The final path finding algorithm is optimized by the filter operation that the calculation is only performed at the endpoints and hub points, which can further reduce computing data amount. In our experiment, 3 368 nodes out of 22 401 nodes are selected as key nodes, therefore, the data processing amount of the algorithm is reduced to 1/7 and the routes can be found in real time. The algorithm is implemented and integrated into the final digital mine system.