Sputtering of W Mo alloy under ion bombardment

The distribution of plasma density in the vicinity of the W Mo alloy source in the process of double glow discharge plasma surface alloying was diagnosed using the moveable Langmuir probe. The sputtering law, surface composition and morphological variation of the W Mo alloy source was studied. The experimental results show that there exists obvious preferential sputtering on the surface of the W Mo alloy source under the argon ion bombardment; the stable period is reached after a transitional period, and the preferential sputtering occurs in a definite range of composition(mole fraction): 70%～75% Mo, 22%～25% W; there appears segregation on the surface of the W Mo alloy source.

EXPERIMENTAL INVESTIGATION AND COMPUTER SIMULATION ON DYNAMIC BUCKLING BEHAVIOR OF LIQUID-FILLED CYLINDRICAL SHELLS UNDER AXIAL IMPACT

This article reports an experimental investigation on the axial impact buckling of thin metallic cylindrical shells fully filled with water. Low velocity impact tests are carried out by DHR-9401 drop hammer rig. The whole process of dynamic buckling is simulated using LS-DYNA computer code. The consistency between experimental observation and numerical simulation is quite satisfactory. The investigation indicates that quite high internal hydrodynamic pressure occurs inside the shell during the impact process. Under the combined action of the high internal pressure and axial compression plastic buckling occurs easily in the thin-walled shells and buckling modes take on regular and axisymmetric wrinkles.

THE GLOBAL DEFORMATION AND LOCAL DAMAGE ANALYSIS OF FILLED METALLIC CYLINDRICAL SHELLS IMPACTED BY MISSILES

A group of theoretical models has been developed for analyzingtransient dynamic re- sponse to filled metallic cylindrical shellsimpacted by flat-nosed missiles at normal obliquity on the ba- sis ofthe analogy modeling method of beam-on-foundation. It can be used forsolving the global defor- mation and the local failure of cylindricalshells in the impact process. the ballistic limit speed and im- pactresponse history have been calculated by this group of theoreticalmodels, and the inner pressure effect on the ballistic limit speedand some parameters are discussed at length.

Age-hardening of surface aged hardening alloy

Steel T8 treated by plasma surface decarburizing was alloyed by the Xu Tec process with Co,W and Mo. An alloyed layer of Fe Co W Mo with low carbon content was formed on the surface of the high carbon steel, thus an advanced gradient composite was produced. The specimens then were treated by the solution and aging treatments. The characteristics of age hardening of the alloying layer were studied. The hardness of the surface layer increases from HV200 to HV1 200 after the solution treatment at 1 190 ℃ and aging at 400 ℃ for 30 min. The results show that the surface aged high speed steel possesses not only high surface hardness, but also enough bulk strength. [

RUPTURE OF THIN METAL TUBES BY NORMAL AND OBLIQUE IMPACT OF BLUNT CONICALNOSED MISSILES:EXPERIMENTS

Impact tests at both normal and oblique angles of incidence were conducted on thin mild tubes using a moderate size of 90 degrees conical-nosed missiles. The minimum impact speed that generated cracks through the thickness of the wall, termed the speed for rupture, was measured, and various modes of rupture were identified. For a thin tube hit by a missile at a normal angle of obliquity at the speed for rupture, the contact region spreads across the nose of the missile, and the transverse shear deformation is predominant in the final failure process. If the angle of obliquity is 30 degrees, the missile pierces a hole through the wall of the tube. At the speed for rupture, the kinetic energy of the missile for oblique angle 30 degrees is only about 45% that required for plugging at a normal angle of obliquity.

AN IN-SITU STUDY ON DISLOCATION BEHAVIOR OF CRACK-TIP IN Ti_3Al-Nb ALLOY

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ELASTO-PLASTIC BRANCHED ANALYSIS FOR AN INTERFACE CRACK BASED ON CRACK ENERGY DENSITY

The elasto-plastic finite element analyses for an interface crack in dissimilar material, based on the crack energy density (CED) concept, are investigated in mode I loading condition. It is confirmed that the values of CED almost remain stable when the notch radius rho is sufficiently small, both in elastic and elasto-plastic case. Numerical results for both elastic and elasto-plastic cases show that under the mode I loading condition, when the crack propagates to the more stiff material with a small angle, the total CED will become larger than that along the interface. If the clack heads into the more compliant material, the CED will become less than that along the interface.

CHAOTIC BEHAVIOR IN THE NONLINEAR ELASTIC BEAM

The dynamic response of the non-linear elastic simply supportedbeam subjected to axial forces and transverse periodic load isstudied. Melnikov method is used to consider the dynamic behav- iorof the system whose post-buckling path is steady. The effect of thehigher order terms in the con- trolling equation is taken intoaccount. It is found that the fifth-order terms have a greatinfluence on the dynamic behavior of the system. The result showsthat there exist either homoclinic orbits or hete- roclinic orbits inthe system. In this paper, the critical values of the system enteringchaotic states are given. The diagram of an example is shown.

Wear Properties of Plasma Nitrided H13 Steel at Room and Elevated Temperature

H13 steel was nitrided using a plasma surface alloying technique at the temperature of 570℃.The nitrided layers with different thicknesses and components were obtained by changing nitriding pressure.The microstructure and composition of the nitrided layers were evaluated by optical microscopy(OM)and X-ray diffraction(XRD).The wear properties of the nitrided layer against Al2O3 ball at room temperature using a ball-on-disc tribometer and against Si3N4 ball at elevated temperature using a HT-2001 abrasive wear test machine were investigated.The results show that the nitrided layers are composed of compound layer and diffusion layer at the pressure of 100 and 450 Pa.No obvious compound layer appears at pressure of 200 and 300 Pa.XRD analysis shows the nitrided layers are mainly composed ofε-Fe2-3N,γ'-Fe4N,α-Fe,Fe2O3 and Fe3O4 phases.The surface hardness of plasma nitrided H13 steel is about 1100HV0.050 doubled that of substrate.The room temperature friction coefficient of H13 steel is reduced and wear rate is decreased by nitriding at 200 and 300 Pa.Elevated temperature wear test indicates the nitrided H13 steel at the pressure of 100 Pa shows lower friction coefficient and wear rate which are reduced more than 6 times compared with that of H13 substrate.

Microstructure and Tribological Behavior of Cr-Cu-N Coatings Deposited by Ion Beam Assisted Magnetron Sputtering

Cr-Cu-N coatings with copper content from 0 at%to 6.8 at%were deposited on silicon and M2 steel by ion beam assisted magnetron sputtering.The microstructure and composition of the coatings were characterized using SEM,GDOES,XRD and XPS.The mechanical properties of the coatings were tested on a standard hardness tester.The tribological behavior of the coatings in dry wear condition was studied by means of ball-on-disc wear test.The experimental results show that addition of copper can restrict the columnar crystal growing to a certain degree.XRD and XPS analysis indicate that coatings are mainly composed of Cr and CrN phase.Cu is mainly existed in a free state in the coatings.Copper adding has no obvious effects on the hardness of the coatings.However,the coatings fracture toughness can be improved by doped copper.The coefficient of friction of the coatings against bearing steel is in the range of 0.25-0.6 changing with the copper content.The coating with 2.6 at%copper shows the lowest coefficient of friction about 0.25 and wear rate which is about one tenth of that of the coating with 6.8 at%copper.The higher coefficient of friction and wear rate of the coating with 6.8at%copper may be attributed to its lower bonding strength.