Abstract: The current situation of experimental investigation on thermal-mechanical fatigue of metal materials are discussed. The test method and performance of thermalmechanical fatigue are analyzed. The research direction and problems existing in thermalmechanical fatigue test and research are proposed.
Abstract: Some of the recent results in the spray forming field performed in University of Science and Technology Beijing are introduced, with an emphasise on the microstructure and mechanical properties of some advanced spray deposited materials including Ni3Al alloys and 26l8Al+SiC particulate reinforced metal matrix composite. These results are typical to the study of spray deposited materials.
Abstract: Spray forming is a new near-net shape preform processing technique for various materials. This technique has begun to realise industrialisation in recent years.Because of its one-step rapid solidification formation feature, spray forming becomes a powerful tool for research and development of new materials. Great attentions have been paid on the development and application of this new technology around the world. Thespray fonning process has been demonstrated as a promising low cost processing technique for high performance materials. In this paper, recent progress of spray formin gprocess and its applications in material science and engineering have been reviewed.
Abstract: A concept of "Vertual" solidification layer is applied to establish a theoretical model to simulate the temperature distribution, solidification time and thickness of the vertual solidication layer during the solidification process in preform during spray forming.Using mathematical simulation methods, these factors mentioned above are solved.
Abstract: According to the solidification model in the spray formed preform, the solidification behavior of typical Al-Cu alloy is calculated and discussed. The result shows that processing parameters such as deposition rate and spray temperature at deposition, and material thermal physical properties such as surface heat transfer coefficient have apparent effects on solidification process in preform. Under the same deposition thermodynamic state just before the spray cone depositing on the surface of the preform, temperature of deposition surface varys significantly as the processing parameters and material thermal physical properties change.
Abstract: The relationship between the structural stability and the long-range-order parameter in the binary alloys is studied using effective atom model based on the pair potential. A analytic equation of the cohesive energy against the long range parameter is given. As a result, the order-disorder transformation of B2 phase is much difficultly to be reached than that of L12 phase intrinsically in the same binary alloy system.
Abstract: The order-disorder transitions of stoichiometrical AB and A3B alloys were studied by using effective-atom model based on EAM (embedded atom method) potential.The results give the analytic function form of the free energy in term of the long range order (LRO) parameter,and indicate that order-disorder transition behaviors of stoichiometrical AB and A3B alloys may be different. This method can be applied to interpret the experimental results of order-disorder transition in stoichiometrical NiAl and Ni3Al.
Abstract: The effective atom model based on EAM potential was applied to study the relationship between the structural stability and the long range order parameter of non-stoichiometrical Ni3Al based alloys. The calculated results indicate that the order-disorder transition temperature (Tt) increases with Al composition increasing. The order-disorder transition process is a nucleation-propagation process. The microstructure of partially order state is a mixed microstructure with full disorder and full order domains. The calculated results are consistent with the experimental results.
Abstract: Dynamic recrystallization behaviours of Al-Mg alloys during hot deformation are investigated by means of polarized light microscopy and electron microscopy.The results show that dynamic recrystallization taks place in a certain range of parameter Z in Al-2Mg and Al-6Mg alloys and dynamic recrystallization behaviour of Al-9Mg alloy is similar to those materials having a lower stacking fault energy. Dynamic recrystallization is accelerated by increasing Mg content, which results from that Mg atmospheres impede cross slip of dislocation, so that dynamic recovery is difficult to cccur.
Abstract: The energy of different Nb disordering and ordering substitution in TiAl with various composition is calculated using the pair-wise potential model. It is observed that the Nb atoms situated on the Ti sublattice in TiAl, and the increasing of Nb and Al contents is beneficial for the ordering occupation of Nb atoms.
Abstract: The formation energy of all possible ordering structures formed by different Nb occupation in Ti sublattice of TiAl with various composition is calculated using the pair-wise potential model. The Nb occupation way with minimum energy is found. The rules of Nb occupation with different Al content were obtained.
Abstract: Artificial neural networks for the Osprey process based on back-propagation are established and some tests are conducted. The relationship between the processing parameters and the outputs are simulated with the networks. It is shown that neural networks are successfully used to pridict porosity values of the process.
Abstract: The spray forming process is simulated. The in-flight dynamical and thermal histories of the droplets during forming process are described. The relation of the independent parameters such as vilocity, temperature, and solid fraction of the droplets to the melt superheat and the gas velocity is established. Based on the calculation of Al-4.5%Cu alloy, the effect of some dependent parameters on the process are discussed.
Abstract: A finite difference method is adapted to simulate liquid metal flow in delivery tube of spray forming. Numerical calculations of minimum superheat, (which is needed to avoid delivery tube blockade due to metal premature solidification), are conducted for different liquid metals (Fe, Zn, Al), and process parameters. A semi-quantitative correlation is derived. Based on the calculated results, for the minimum superheat, the heat conductivity of delivery tube is the most imortant factor, a inapppropriate selection of tube materials will cause superheat beyond permission; increasing overpressure also can decrease minimum superheat significantly; the other critical factor is the design of delivery tube configuration, reducing the length/diameter ratio (L/D) can decrease minimum superheate, specially for metals with high melting point or delivery tube with high thermal conductivity.
Abstract: High coercivity, high remanence, and high energy product (NdDy)2(FeNb)14B/α-Fe nanocrystalline alloys are prepared by melt spining and subsequent annealing. The best properties of remanence (Br), coercivity (Hci) and maximum energy product ((BH)max) are 1.02 T, 702 kA/m and 134 kJ/m3, respectively. The microstructure of the two phase nanocomposite consists of hard magnetic (NdDy)2(FeNb)14B and soft magnetic α-Fe with an average size of 30 nm. These small dimensions allow effective exchange coupling between hard and soft magnetic grains and result in the simultaneous enhancement of Br,Hci and (BH)max.
Abstract: The structural changes of nonequilibrium interlamellar boundaries with a relatively high strain energy during subsequent 800℃, 15 min, WQ and 1000℃, 4 min, WQ annealing were studied by the conventional and high resolution transmission electron microscopy in the hot-forged Ti-45Al-8Nb-2.5Mn-0.05B alloy. The structural relaxations are mainly as following:further bending of interlamellar boundaries, necking and spheroidization process of α2 plates, formation of subgrain boundaries within γ plates, etc..
Abstract: The crystallographic orientation, morphologies and the relationship between the orientation and magnetostrictive properties of directionally solidified Laves-phasee Tb0.3Dy0.7 (Fe,M)1.95 alloys by zone melting with high thermal gradient GL wre studied.With increasing in Laves-phase growth vilocity at a high GL given, it is shown that the solidification structure of alloys are from planar to cellular and to final dentritic structure,and meanwhile the crystallographic orientation of the Laves-phase are various correspondently. The optimum magnetostrictive properties of the alloys with perfect <112> axial orientation are obtained.
Abstract: Amorphous phase was obtained by mechanical alloying of Ti-Al-Si powders with four different composition. The structure evolution of the as-milled amorphous phase during the annealing treatment is classified into three stages:the first is partial crystallization of amorphous phase producing Ti5Si3 phase; the second is crystallization of the rest amorphous phase producing the corresponding titanium aluminides according to the relative amount of Ti and Al in the elemental mixture; and the last one is grain growth of all the phase in powders. The crystallization result in formation of Ti3Al,TiAl and Al3Ti according the powder composition. Ti5Si3 is the only silicide produced by crystallization reaction. The annealing treatment (less than 800℃ for A3, A4 and A5, and 750℃ for A6) shows that the grain size of all the phases fall in nanometer range.
Abstract: Applying ny sputtering techniques, a series of fcc (Fe1-xNix/Cu)10 superlattices are prepared with Ni concentrations x ranging from 0.26 to 0.54. The use of MgO single crystal substrates and Cu sublayers in the superlattice growth ensure well defined fcc crystal structures in the Fe-Ni sublayers with a Ni concentration as low as 26% and down to liquid helium temperatures.The magnetization of the Fe-Ni sublayers in the super-lattices is reduced when the composition of the Fe-Ni layers approaches the Invar composition, i.e., it shows a deviation from the well-known Slater-Pauling curve. Strong dependence of magnetization on temperature is also observed for the Fe-Ni sublayers with Invar compositions, consistent with the behavior of the bulk Fe-Ni Invar alloys. It is concluded that the deviation of magnetic moment of FeNi alloys near the Invar composition may not be attributed to the so-called premartensitic transformation, but to the Fe-Fe antiferromagnetic interactions in the alloys.
Abstract: CNx films have been prepared by DC magnetron sputtering of graphite in pure nitrogen atmosphere. N/C ratio is between 0.21 and 0.42, strongly correlating with deposition parameters. The hardness and modulus are related not only to the N/C ratio,but also to the formation and the amount of C≡N triple bonds in the CNx films. High bias voltage and high sputtering power are beneficial to the increase of C≡N bands and so are helpful to increase the hardness and bulk modulus.
Abstract: Influence of heat treatment process on shape memory effect (SME) inFe-28Mn-4Si (adding microelement Magnesium) alloy were studied. The results show thatSME of alloy originates from stress induced γ-ε martensitic transformation and itsreversible transformation, SME can be improved by thermal mechanical training treatmentand solution treatment by strengthening austenitic matrix. When the inside diameter of hotrolled seamless alloy pipes is expended by 5%, the strain recovery ratio will be 45%, andthis strain recovery ratio is enough for pipe joints.
Abstract: The reactive characteristics of multi-component thermit, Fe2O3-CrO3-NiO-Al, were studied in detail by thermal analytical technique. The thermal properties of CrO3, play an important role in the thermit reaction and effect on the composition of reaction products.
Abstract: The magnetization feature under high magnetised fields and the effect of magnetised field on demagnetization behaviour for Nd4Fe77.5B18.5 nanocrystalline alloy were investigated. The results indicate that the alloy is not saturated magnehsed while magnetization-field μOHm=7 T. The material shows typical characteristics of permanent magnet as magnetization-field Hm is larger than a critical magnetization field Hmc. The permanent magnet features of this alloy origine from exchange-coupling inteaction between crystalline grains.
Abstract: Stress-strain curves on Gleeble-1500 machine are given. Some factors influencing the test results actually, such as temperature gradient, lubrication conditions,control mode and the specimen's size, are investigated. Based on the experimental data,the relationship between these factors and the measurements of stress-strain curves are discussed.
Abstract: A new method of determinning the threshold value △Kth on a new type AMSLER fatigue test system by computer control is given. By using this method, △Kth can be obtained after the material has been fatigued a given cycles under constant stress ratio R, on condition that the decreasing of frequency is less than a certain value.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
