Zi Dong Wang

Microstructure and Properties of ZcuSn3Zn8Pb6NiFeCo Alloy

In Situ iron nanoparticles can be formed during copper alloy solidification. Here we consider ZCuSn3Zn8Pb6Ni1FeCo alloy.It is noted that high undercooling is the motive power of nanoparticles during solidification , which would act as heterogeneous nuclei to achieve outstanding contribution for grain refinement compared to ZCuSn3Zn8Pb6Ni1 alloy. Convection of the melt inhibit the growth of nanoparticles by way of prohibitting the deposition of iron atoms on the surface.This technique offer new enlightenment for the control of in-situ nanoparticles formed during alloy solidification,and also opens the door to a new class of dispersed nanoparticles strengthened materials.

Effect of Aging Process on Organization and Performance of Cu-Cr-Zr-Mg Alloys

The organization and performance of Cu-0.4Cr-0.2Zr-0.15Mg alloy after solution treatment at 960°C for 2h, and then cold-rolled to deformations of 80%, finally aging treatment from 400°C to 500°C in argon atmosphere for various periods from 4h to 16h prior to air cooling were analyzed. Eventually the optimum process was aging at 475°C for 16h. At this process condition, the alloy had an excellent comprehensive mechanical properties and conductivity property of the tensile strength, elongation, and electrical conductivity reaching 549MPa,15% ,and 82.34%IACS respectively. The microstructure of alloy with the best aging process was analyzed by SEM and EDS and TEM shows that the separation phase distributed diffusely on matrix. the main separation phase is Cr phase which mainly exists as simple substance form after age treatment ,the fraction Cr phase forms intermetallic compound with Cu,Zr,Mg. The other phase (as Zr,Mg) exists as intermetallic compound form. The Zr phase doesnt exist as simple substance form.

Study of Nano-Precipitate in High Strength Low Carbon Steel during Tempering by TEM

The behavior of nanoprecipitates of 800Mpa grade high strength low carbon steel during tempering has been studied. Transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive spectrometry (EDS) were used to systematically analyze the morphology of precipitates and their grain orientation with matrix at different tempering temperatures. Experimental results confirm that the composition of these nanometer sized particles in the matrix was compound carbonitrides containing Ti, V, Mo and other elements. The precipitates of the as-received steel are (Nb,Ti)(C,N) at low tempering temperature, while those at high tempering temperature are composite carbides containing a variety of elements such as Mo, V, Ti and Nb. On the other hand, as tempering temperature increases, precipitates in the steel were slowly growing up and roughening according with the typical Oswald ripening mechanism; a sharp orientation relationship exists between precipitates and matrix.

The Interaction of the Convective Flow with the Interface Evolution of the Particle Growing in the Undercooled Melt

This paper investigates the interaction between the convective flow induced by the straining flow and the interface morphology of a particle growing in the convective undercooled melt. The resulting approximate solution of the particle shape shows that the convection makes the growing particle enhance its growth velocity and protrude near the surface where the flow is incoming, but decreases its growth near the surface where the flow is outgoing, and both the incoming flow and the anisotropic surface tension make the velocity of the particle have a superposition effect along the favorite crystalline direction. The convection makes the particles growing in the undercooled melt evolve into various shapes of the interface morphology which have high strength/weight ratio and specific surface fraction and then help to form the final material of excellent mechanical and physical properties.

Effect of Heat Treatment on Microstructure and Mechanical Properties of 800MPa Grade Ultra Low Carbon Bainite Steel

A new kind of bainite steel with ultra-low carbon content and Nb, Ti alloys has been developed. By applying thermomechanical control process, water quenching and tempering at different temperature, excellent properties have been obtained when tempered at 450°C, with the yield strength of 813MPa and elongation of 16.2%. The morphology observed by SEM shows that the microstructure consists of fine lath-shaped bainite, polygonal ferrite, quasi-polygonal ferrite and a small fraction of residual austenite or martensite-austenite constituents. In a TEM study plenty of precipitates with the size about 5-10nm were observed interacting with the dislocations, which is very significant for the optimization of strength and ductility.

Investigation of the Precipitation in Mg-Zr Alloys

The Mg-Zr alloys with the Zr contents of 0.2%, 0.4%, 0.6% and 0.8% were prepared using induction melting, metal mold centrifugal casting process. The microstructures of the alloys were analyzed by scanning electron microscope, energy spectrum analysis, transmission electron microscope and their mechanical properties were also measured with tensile test. The results show that there are many micro- and nano-sized Zr-rich or Zr particles dispersed in Mg-Zr alloys. The nano-sized Zr-rich particle consists of a rectangle shaped Zr core and its surrounding Mg (Zr) solid solution shell with round exterior; a single Zr particle appears a coherent lattice relationship with matrix.

Mathematical Model of Unidirectional Solidification with Mushy Layer

The general mathematical formulation under unidirectional solidification with mushy layer is developed. For the steady state of solidification, concentration and temperature fields in the mushy region are given as functions of a solid volume fraction. The nonlinear model of solidification in mushy zone is changed into system of the second order ordinary differential equation with free boundary conditions, which is solved using numerical calculating method. Solid volume fraction at the solid-mush interface is also obtained. For fixed control conditions, mushy layer width of Fe-Ni alloy in unidirectional solidification is predicted.

The Influence of Fe on the Strength and Ductility of Cu-10Sn-2Zn Based Alloys

The In situ iron nanoparticle reinforced Cu10Sn2Zn alloy was fabricated by centrifugal casting in vacuum chamber with a medium frequency electrical furnace. The major challenge in development of this alloy is to fide an approach to strengthen copper alloys with the increase of ductility. In this paper, we fide an effective way to balance the strength and ductility by identifying three essential structural characteristics for nanoparticles: in-situ formation in molten metal, smallest feature size finer than 10 nanometers and coherency with surrounding matrix. The tensile strengths and the elongation of ZCuSn10Zn2+Fe1.5% were 550Mpa and 42%respectively, which were remarkably improved compared to ZCuSn10Zn2.

Analytical Solution of Mushy Zone under Directional Solidification

Based on the general mathematical formulation under unidirectional solidification with mushy layer developed in Ref.[13], leading approximation of solution in mushy layer is obtained for the case that the inverse Lewis number is small parameter. For the steady state of solidification, concentration field in the mushy region is given as function of a solid volume fraction. Mushy layer width and solid volume fraction at the solid-mush interface are obtained. Effects of temperature gradient on mushy layer width and solid volume fraction at solid-mush interface are presented.

Effect of Aging Temperature on the Microstructure and Mechanical Properties of 1000MPa Grade Low Carbon Bainitic Steel

A kind of 1000MPa low carbon bainitic steel belonged to the Fe-Cu-Nb series was hot rolled and aged, the influence of aging temperatures on the microstructure and mechanical properties of the steel were investigated by using Scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The results show that the microstructure of the low carbon bainitic steel consisted of lath-shaped bainite(LB), granular bainite(GB) and quasi-polygonal ferrite(QF), and the proportion of each kind of microstructure changed with the aging temperatures. The strength of steel with the increase of aging temperature first increased, then decreased, Aging temperatures had distinct effect on yield strength of the tested steel, and less effect on the ultimate tensile strength, we can get the best comprehensive properties yield strength 1011.87 MPa and elongation rate 16.38% of good tough match aged at 450°C. Through analysis it is concluded that the strength of the tested steels aged at 450°C reaches the maximum value, which is attributed to the precipitation of a large amount of fine ε-Cu particles(5~10nm) and a small number of(Nb,Ti)(C,N) precipitates.