强化金融力度推进科技进步

强化金融力度推进科技进步熊国胜（中国工商银行长沙市分行芙蓉路分理处）充分发挥我国的科技优势，确立科技进步战略，无疑离不开金融业的支持。本文通过对我国科技进步中的资金问题进行分析、讨论，探求运用金融手段推动我国科技进步的有效途径和策略。一、实证分析邓小...

MACHINING OF METAL MATRIX COMPOSITES

Two types of aluminium-based composites reinforced respectively with 20 vol short fibre alumina and with a hybrid of 15 vol SiC particle and 5 vol short alumina fibre are machined with different tool materials:cemented carbide,ceramic,cubic boron nitride(CBN)and polycrystalline diamond(PCD).The analysis on tool wear shows that the various tool materials exhibite different tool wear behaviours,and the tool wear mechanisma are discussed.Apparently,PCD tools do not necessarily guarantee dimensional stability but they can provide the most economic means for machining all sorts of composites.Consequently,a suitable tool material is suggested for machining each metal matrix composite(MMC) from the standpoints of tool wear and machined surface finish.

High Pressure Phase Stability of Ti with Self-consistent ab initio Lattice Dynamics Approach

The traditional quasiharmonic approximation cannot predict the phase diagram of Ti accu- rately, due to the well-known soften phonon modes of the β-Ti. By means of self-consistent ab initio lattice dynamics （SCAILD） method, in which the effects of phonon-phonon in- teractions are considered, the phonon dispersion relations at finite temperature for Ti are calculated. From the phonon dispersions, we extrapolat the acoustic velocities and harmonic elastic constants. The dynamical stable regions and phase diagram of Ti are also predicted successfully. The results show that SCAILD method can be designed to work for strongly anharmonic systems where the QHA fails.

Distribution and Migration of Heavy Metals in Undisturbed Forest Soils:A High Resolution Sampling Method

The vertical distribution and migration of Cu,Zn,Pb,and Cd in two forest soil profiles near an industrial emission source were investigated using a high resolution sampling method together with reference element Ti.One-meter soil profile was sectioned horizontally at 2 cm intervals in the first 40 cm,5 cm intervals in the next 40 cm,and 10 cm intervals in the last 20 cm.The migration distance and rate of heavy metals in the soil profiles were calculated according to their relative concentrations in the profiles,as calibrated by the reference element Ti.The enrichment of heavy metals appeared in the uppermost layer of the forest soil,and the soil heavy metal concentrations decreased down the profile until reaching their background values.The calculated average migration rates of Cd,Cu,Pb,and Zn were 0.70,0.33,0.37,and 0.76 cm year-1,respectively,which were comparable to other methods.A simulation model was proposed,which could well describe the distribution of Cu,Zn,Pb,and Cd in natural forest soils.

A numerical method for multiple cracks in an infinite elastic plate

This article examines the interaction of multiple cracks in an infinite plate by using a numerical method. The numerical method consists of the non-singular displacement discontinuity element presented by Crouch and Startled and the crack tip displacement discontinuity elements proposed by the author. In the numerical method implementation, the left or the right crack tip element is placed locally at the corresponding left or right crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. The numerical method is called a hybrid displacement discontinuity method. The following test examples of crack problems in an infinite plate under tension are included： “ center-inclined cracked plate”, “interaction of two collinear cracks with equal length”, “interaction of three collinear cracks with equal length”, “interaction of two parallel cracks with equal length”, and “interaction of one horizontal crack and one inclined crack”. The present numerical results show that the numerical method is simple yet very accurate for analyzing the interaction of multiple cracks in an infinite plate.

A Theoretical Model on Solvus Line Prediction of Film and Its Application in Nanogranular Al-Cu System

A theoretical model on the solvus line prediction of a film was proposed and applied to a nanogranular A1-Cu system. The calculation results show that the solvus line of solute Cu will markedly lower with the decrease of grain size, namely, the starting temperature of θ （Al2Cu） precipitation in a nanogranular A1-Cu film will markedly lower than that of conventional coarse grain alloy with the same Cu concentration, and the precipitation temperatures calculated are comparable with the experimental ones. The theoretical model can be simply used to calculate the starting temperature of precipitation in A1-Cu films under three states： ① films with substrate; ②films without substrate; ③ultrafine grain bulk alloy. As a result, the model is universal, moreover, can be, in principle, used to predict precipitation temperature in other systems.

Enhanced mechanical properties of lamellar Cu/Al composites processed via high-temperature accumulative roll bonding

Cu/Al multilayers were produced by high-temperature accumulative roll bonding(ARB)methods up to three passes.To achieve a high bonding strength,prior to ARB processing,the Cu and Al sheets were heated to 350,400,450 and 500 ℃,respectively.The mechanical properties were evaluated by tensile tests.The microstructure was examined by optical microscopy and scanning electron microscopy equipped with energy dispersive spectrometry.The ultimate tensile stress,the grain size and the thickness of diffusion layer of lamellar composites increase with rolling temperature.When the rolling temperature is 400 ℃,the laminates show the highest ductility,but the yield stress is the lowest.As the rolling temperature further increases,both the yield stress and the ultimate tensile stress increase and the ductility decreases slightly.The mechanical properties of lamellar composites processed by low and high temperature ARB are determined by grain size and the thickness of diffusion layer,respectively.

Analysis of complete plasticity assumption for solid circular shaft under pure torsion and calculation of shear stress

The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding, the applicability of complete plastic model assumption and the shear stress formula were researched. Based on the shear stress formula of circular shaft under pure torsion in elastic stage, the formula of torque in elastic stage and the definition of yield, it is obtained that the yielding stage of plastic metal shaft under pure torsion is only a surface phenomenon of torque-torsion angle relationship, and the distribution of shear stress is essentially different from that of tensile stress when yielding under uniaxial tension. The pure torsion platform-torsion angle and the shape of torque-torsion angle curve cannot change the distribution of shear stress on the shaft cross-section. The distribution of shear stress is still linear with the maximum shear stress ts. The complete plasticity model assumption is not in accordance with the actual situation of shaft under torsion. The experimental strength data of nine plastic metals are consistent with the calculated results of the new limiting strain energy strength theory （LSEST）. The traditional yield stress formula for plastic shaft under torsion is reasonable. The shear stress formula based on the plane assumption in material mechanics is applicable for all loaded stages of torsion shaft.

Computer simulation for the effect of coherent strain on the precipitation progress of binary alloy

Based on the microscopic elasticity theory and microscopic diffusion equation, the precipitation progress of the binary alloys including coherent strain energy was studied. The results show that coherent strain has obvious effect on the coherent two-phase morphology and precipitation mechanism. With the increase of coherent strain energy, the particles shape changes from the randomly distributed equiaxed particels to elliptical precipitate shapes,their arrangement orientation increases; in the late stage of precipitation, the particle arrangement presents obvious directionality along the [10]and[01]directions, and the precipitation mechanism of alloy changes from typical spinodal decomposition mechanism to the mixture process which possesses the characteristics of both non-classical nucleation growth and spinodal decomposition mechanisms.

In situ atomistic mechanisms of detwinning in nanocrystalline AuAg alloy

Detwinning is an important plastic deformation mechanism that can significantly affect the mechanical properties of twin-structured metals.Although many detwinning mechanisms have been proposed for pure metals,it is unclear whether such a deformation model is valid for nanocrystalline alloys because of the lack of direct evidence.Here,the atomicscale detwinning deformation process of a nanocrystalline AuAg alloy with an average grain size of~15 nm was investigated in situ.The results show that there are three types of detwinning mechanisms in nanocrystalline AuAg alloys.The first type of detwinning results from grain boundary migration.The second type of detwinning occurs through combined layer-by-layer thinning and incoherent twin boundary migration.The last one occurs through incoherent twin boundary migration,which results from the collective motion of partial dislocations in an array.

Calculation of Half-Metal, Debye and Curie Temperatures of Co_2 VAl Compound: First Principles Study

By FP-LAPW calculations, the structural, elastic, Debye and Curie temperatures, electronic and magnetic properties of Co2 VAl are investigated. The results indicate that Ferromagnetic （FM） phase is more stable than Anti- Ferromagnetic （AFM） and Non-magnetic （NM） ones. In addition, C11-C12 〉 0, C44 〉 0, and B 〉 0 so Co2 VAl is an elastically stable material with high Debye temperature. Also, the BIG ratio exhibits a ductility behavior. The relatively high Curie temperature provides it as a favorable material for spintronic application. It＇s electronic and magnetic properties are studied by GGA ＋U approach leading to a 100% spin polarization at Fermi level.

Defects production and mechanical properties of typical metal engineering materials under neutron irradiation

Maintaining the safety and reliability of nuclear engineering materials under a neutron irradiation environment is significant. Atomic-scale simulations are conducted to investigate the mechanism of irradiation-induced vacancy formation in CLAM, F82 H and α-Fe with different neutron energies and objective laws of the effect of vacancy concentration on mechanical properties of α-Fe. Damage of these typical metal engineering materials caused by neutrons is mainly displacement damage, while the displacement damage rate and the non-ionizing effect of neutrons decrease with the increase of neutron energy. The elastic modulus, yield strength, and ultimate strength of α-Fe are in the order of magnitude of GPa. However, the elastic modulus is not constant but decreases with the increase of strain at the elastic deformation stage. The ultimate strength reaches its maximum value when vacancy concentration in α-Fe is 0.2%. On this basis, decreasing or increasing the number of vacancies reduces the ultimate strength.