升温速率对Micro-FAST制备锰锌铁氧体磁芯显微组织及性能的影响

采用多物理场耦合烧结技术(Micro-FAST)烧结制备了MnZn铁氧体U型磁芯零件,研究了升温速率对MnZn铁氧体磁芯的微观组织和性能的影响。结果表明:在升温速率30℃/s、压力75 kg、烧结温度900℃、保温时间360 s的条件下,烧结制备磁芯的密度4.87 g/cm^(3)、饱和磁化强度55.78 emu/g、剩磁1.59 emu/g、矫顽力14.83 Oe、电阻率3.88Ω·m。适当提高升温速率,可增大磁芯的密度、减少孔隙、促进尖晶石相晶粒的形核与生长以及微观组织均匀完整,从而有利于提高MnZn铁氧体磁芯的磁性能。

Microstructures,micro-segregation and solidification path of directionally solidified Ti-45Al-5Nb alloy

To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb(at.%) alloy, Bridgman-type directional solidification and thermodynamics calculations were performed on the alloy. The microstructures, micro-segregation and solidification path were investigated.The results show that the β phase is the primary phase of the alloy at growth rates of 5-20 μm·s^(-1) under the temperature gradients of 15-20 K·mm^(-1), and the primary phase is transformed into an α phase at relatively higher growth rates(V >20 μm·s^(-1)). The mainly S-segregation and β-segregation can be observed in Ti-45Al-5Nb alloy at a growth rate of 10 μm·s^(-1) under a temperature gradient of 15 K·mm^(-1). The increase of temperature gradient to 20 K·mm^(-1) can eliminate β-segregation, but has no obvious effect on S-segregation. The results also show that 5 at.% Nb addition can expand the β phase region, increase the melting point of the alloy and induce the solidification path to become complicated. The equilibrium solidification path of Ti-45Al-5Nb alloy can be described as L L→β L+β L+β→αα+β_R β→ααα→γα+γα→α_2+γγ_R+(α_2+γ), in which β_R and γ_R mean the residual β and

Microstructures and properties of rapidly solidified Mg-Zn-Ca alloys

Ternary alloys based on the Mg-Zn-Ca system were produced by twin-roll rapid solidification.The alloys were characterized by OM,SEM,HRTEM,XRD,EDS and Micro-hardness.The results show that the rapidly solidified flakes are of fine dendritic cell structures with the cell size ranging from 1 to 5μm.The Mg-6Zn-5Ca alloy in RS and annealing(200℃for 1 h) states are mainly composed ofα-Mg,Mg_2Ca,Ca_2Mg_6Zn_3 and a small quantity of Mg_(51)Zn_(20),MgZn_2 and Mg_2Zn_3.Micro-hardness increases with the increment of Ca content and age hardening occurs after aging at 200℃in the flakes probably due to the precipitation strengthening of the fine precipitates Mg_2Ca and Ca_2Mg_6Zn_3.Some phases at the grain boundary in Mg-6Zn-5Ca alloy are identified by means of HRTEM,which may be beneficial to the improvement in thermal stability of the alloy.

Effects of Yttrium on Mechanical Properties and Microstructures of Ti-Si Eutectic Alloy

The effects of rare earth （Y） on Ti-TisSi3 eutectic alloy are studied. The results of microstructure analysis show that the colonies and microstructures of the raw alloy are transformed evidently with the addition of Y. With proper addition of yttrium （0.025at%）, the shape and size of the coarse TisSi3 phases of the colonies change to be fine and round meanwhile the microstructure of the alloy goes into uniformity. The compressive ductility and strength at room temperature are also improved. The effects of yttrium on the alloy are likely due to that Si atoms in TisSi3 phase are partially substituted for yttrium atoms which results in silicide Ti5（Si, Y）3 phases.

基于Micro-CT评价温阳补肾方对兔激素性股骨头坏死模型股骨头微结构的影响

目的:通过Micro-CT图像评价温阳补肾方对兔激素性股骨头坏死模型股骨头骨量的影响。方法:选取健康雄性新西兰大白兔6只,分成空白组、模型组、中药组(温阳补肾方临床等效剂量组)。用马血清加甲基强的松龙的方法建立兔激素性股骨头坏死模型,同时正常组等量注射生理盐水。造模结束后,正常组与模型组予生理盐水灌胃,治疗组则给予温阳补肾方灌胃,第四周处死所有兔子取材双侧股骨头,用Micro-CT扫描图像进行分析和评价。结果:大体形态观察:模型组股骨头破损变薄,骨质脆弱,软骨面颜色苍白,表面粗糙;中药组与模型组相比,股骨头破损程度较降低,软骨面颜色较白,骨质较硬,与正常组相比,光泽度较弱。Micro-CT图像显示:模型组股骨头变形,骨皮质不连续且较正常组薄弱,骨质密度不均,“星芒征”消失;软骨面可见剥脱裂纹,骨小梁排列紊乱,甚至断裂;中药组各个骨组织形态与正常组接近;与模型组相比,股骨头外形饱满;骨小梁的排列趋于规则,软骨层增厚,骨皮质连贯。结论:糖皮质激素的大量运用会导致股骨头形态发生改变,主要表现为外形塌陷、骨皮质连续性破坏、骨密度降低、软骨面剥脱、骨小梁紊乱等;温阳补肾方的应用可扭转激素性股骨头坏死的骨组织形态变化,使已变形塌陷的股骨头外形趋于饱满、紊乱的骨小梁排列整齐、恢复骨皮质连续性、增厚薄弱的软骨层。从直观的影像学角度,证明了温阳补肾方在治疗激素性股骨头坏死方面的显著作用。

Micro CT检测小鼠骨微结构指标受标本通量影响的方案设计

在过去几十年中,Micro CT已成为评估小动物骨骼微结构的金标准。然而Micro CT得到的定量指标会受到很多因素影响,如成像参数、重建像素大小和图像分割阈值等。为了提高相关实验准确性和可重复性,以及在各个研究间进行更可靠的比较,结合小鼠离体股骨的Micro CT实验,设计不同通量的标本及组合方案来验证骨微结构测量结果是否受其影响。结果表明,标本通量及组合方式的不同对骨微结构指标测量没有产生显著性影响,但高通量扫描会降低输出图像的质量,可能会减弱组间差异的检测能力,仍需注意其产生的影响。因此在确定实验方案前需探讨标本通量对实验结果是否产生影响,或者在整个研究中保持标本通量和标本摆放方式的一致性。

Microstructure and properties of laser micro welded joint of TiNi shape memory alloy

Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet （SMA） was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.

Effect of homogenization treatment on microstructure evolution and the distributions of RE and Zr elements in various MgeLieREeZr alloys

Mge3Lie0.4Zr alloys containing RE elements(Gd,La,Nd)(Mge3LieREe0.4Zr alloys)are investigated to reveal the influence of homogenization treatment on microstructures and distributions of RE,Zr elements.It is found that 300
C24 h homogenization treatment shows better improvement on the microstructure including the refinement of grain size,the dispersion of cellular dendrite and low melting point particles.Before treatment,La and Nd segregate effectively at grain boundary and Zr segregates in the form of precipitates.Homogenization treatment induces the reduction of RE segregation.However,the segregation of Zr in precipitates cannot be abated due to the relatively low diffusion rate compared with RE elements.

Microstructure and Properties of Graphene Oxide-doped TiO_2 Coating on Titanium by Micro Arc Oxidation

Micro arc oxidation(MAO) coatings doped with graphene oxide(GO) were prepared on pure titanium by adding GO and sodium dodecyl benzene sulfonate(SDBS) into a sodium silicate solution. The as-deposited coatings were comparatively analyzed by scanning electron microscopy(SEM), energydispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD). The binding forces of the MAO, MAO+GO and MAO+GO+SDBS three coatings were measured by a scratch tester. The mechanical property of the three coatings was analyzed using the nano-indentation technique. The corrosion resistance of the coatings was tested by the electrochemical system in 3.5% NaCl solution. The photocatalytic activity of the prepared samples was evaluated by determining the degradation of methylene blue(MB) solution. The results showed that compared to the MAO coating, the morphologies and phase compositions of MAO+GO and MAO+GO+SDBS composite coatings were significantly different. These two composite coatings all had superior photocatalytic activity. Especially, the MAO+GO composite coating still had enhanced binding force and excellent corrosion resistance. Furthermore, the relationship between the microstructure and the properties of these three MAO coatings was analyzed.

Engineering properties and microstructure of expansive soil treated with nanographite powder

To reduce geological disasters caused by expansive soil,it is crucial to use a new type of modified material to rapidly improve soil strength instead of traditional soil improvement materials such as lime and cement.Nanographite powder(NGP)has excellent properties,such as high adsorption,conductivity,and lubrication,since it has the characteristics of small size,large specific surface area,and high surface energy.However,previous studies on the improvement of expansive soil with NGP are not processed enough.To study the improvement effect of NGP on expansive soil,non-load swelling ratio tests,consolidation tests,unconfined compressive strength tests,mercury injection tests,and micro-CT tests on expansive soil mixed with different NGP contents were performed.The results show that the non-load swelling ratio,mechanical properties,and porosity of expansive soil show some increasement after adding NGP.The strength of expansive soil reaches the maximum when the NGP content is 1.450%.The cumulative mercury volume and compressive strain of expansive soil reach the maximum with the 2.0%NGP content.Finally,the modification mechanism of swelling,compressibility,microstructure,and compressive strength of expansive soil by NGP is revealed.

Experimental Investigation on Micro Deep Drawing of Stainless Steel Foils with Different Microstructural Characteristics

In the present work,austenitic stainless steel(ASS)304 foils with a thickness of 50μm were first annealed at temperatures ranging from 700 to 1100℃for 1 h to obtain different microstructural characteristics.Then the effects of microstructural characteristics on the formability of ASS 304 foils and the quality of drawn cups using micro deep drawing(MDD)were studied,and the mechanism involved was discussed.The results show that the as-received ASS 304 foil has a poor formability and cannot be used to form a cup using MDD.Serious wrinkling problem occurs on the drawn cup,and the height profile distribution on the mouth and the symmetry of the drawn cup is quite non-uniform when the annealing temperature is 700℃.At annealing temperatures of 900 and 950℃,the drawn cups are both characterized with very few wrinkles,and the distribution of height profile,symmetry and mouth thickness are uniform on the mouths of the drawn cups.The wrinkling becomes increasingly significant with a further increase of annealing temperature from 950 to 1100℃.The optimal annealing temperatures obtained in this study are 900 and 950℃for reducing the generation of wrinkling,and therefore improving the quality of drawn cups.With non-optimized microstructure,the distribution of the compressive stress in the circumferential direction of the drawn foils becomes inhomogeneous,which is thought to be the cause of the occurrence of localized deformation till wrinkling during MDD.

Characterization of microstructure evolution of cement paste by micro computed tomography

Micro computed tomography (Micro-CT) was applied to obtain three-dimensional images of the microstructure of cement paste (water-to-cement mass ratio of 0.5) at different ages. By using the Amira software, component phases of the cement paste such as pores, hydration products, and unhydrated clinker particles were segmented from each other based on their 3D image grey levels; their relative contents were also calculated with the software, and the data are 61.2%, 0% and 38.8% at the beginning of hydration and 11.8%, 78.5% and 9.7% at 28 d age, respectively. The hydration degree of cement paste at different ages was compared with the experimental data acquired by loss on ignition (LOI) tests. The results show that the calculated and measured data reasonably agree with each other, which indicates that micro-CT is a useful and reliable approach to characterize the micro structure evolution of hydrating cement paste.

Microstructure and Fractural Morphology of Cobalt-based Alloy Laser Cladding

The solidification features,micro segregation,and fracture characteristics of cobalt based alloy on the substrate of 20CrMo steel by laser cladding were studied by using electron microscopy.Experimental results show that the fine columnar grains and cellular dendrite grains are obtained which are perpendicular to the coating/substrate interface;the primary arms are straight while the side branches are degenerated;the microstructure consists of primary face centered cubic (fcc) Co dendrites and a network of Cr enriched eutectic M23C6 (M=Cr,W,Fe) carbides;the micro segregation is severe for the rapid heating and cooling of laser cladding;the typical brittle intergranular fracture occurs in cobalt based laser cladding layer.

Effect of Stirring Velocity in Micro Fused-Casting for Metal on Microstructure and Mechanical Properties of A356 Aluminum Alloy Slurry

A novel micro fused-casting for metal（MFCM） process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizontal movable plate. With the aid of 3D manufacturing software, the melt is solidified and formed layer by layer. The stirring could keep the ingredients and the heat diffusion of metal slurry uniform in the crucible due to the shear force breaking down the dendrite arms. The solidus and liquidus temperatures of A356 alloy were 559.2 and 626.3 ℃, respectively, which were measured by differential scanning calorimetry（DSC）. Effect of different stirring velocities of MFCM on the microstructure and mechanical properties of A356 slurry was investigated with the pouring temperature controlled at 620 ℃. The microstructure and mechanical performance were the best when the stirring velocity was 1 200 r/min in MFCM. The microstructures of the A356 aluminum alloy slurry were mainly composed of fine spherical or rose grains. The average roundness and average grain size reached 2.2 and 41 μm and the tensile strength of A356 alloy slurry reached 207.8 MPa, while the average vickers hardness was 81.1 HV.

Effects of electric parameters on microstructure and properties of MAO coating fabricated on ZK60 Mg alloy in dual electrolyte

Micro-arc oxidation (MAO) process was carried out in a dual electrolyte system of NaAlO 2 and Na 3 PO 4 on ZK60 Mg alloys to explore the effect of electric parameters including current density, frequency, duty cycle and oxidation time on the evolution of coatings and other characteristics. The microstructural characteristics of coatings were observed by scanning electron microscopy (SEM) combined with the analysis of voltage-time responses during MAO process. Test of weight loss was conducted at a 3.5% NaCl solution to assess the resistance to corrosion. The results indicate that the current density and duty cycle play key roles on the coating quality. The peak voltage during MAO process increased with the increase in current density but the coating would be more easily detached when the current density was beyond a critical value. Voltage during MAO and microstructure of the coating were affected remarkably by duty cycle, and corrosion resistance was improved greatly when duty cycle was 40%. By means of single variable experiments, MAO process with optimized electric parameters was developed, which corresponds to the current density of 20 A dm 2 , frequency of 500 Hz, duty cycle of 40% and oxidation time of 15 min.

Investigating microstructure of Longmaxi shale in Shizhu area,Sichuan Basin, by optical microscopy, scanning electron microscopy and micro-computed tomography

Microstructure of shale formation is the key to understanding its petrophysical and chemical properties.Optical microscopy, scanning electron microscopy and micro-computed tomography(μ-CT) have been combined for characterization of microstructure of Longmaxi(LMX)shale from Shizhu area, Sichan Basin. The results indicate that laminated LMX shale consists of mineral matrix-rich layers and organic matter(OM)-rich layers at micrometer scale in two and three dimensions. Mineral matrix layers,mainly consisting of interparticle pores and intraplatelet pores, are approximately parallel to the bedding plane.Pyrite-rich layer, mainly containing intercrystalline pores,shows a strong preferred orientation parallel to the bedding plane. OM-rich layer, mainly containing OM pores, seems to be discontinuous. In addition, intercrystalline pores are enriched in some layers, while OM pores are distributed irregularly in matrix layers. This vertical heterogeneity of pore microscopic structures in LMX shale is of great importance to understand its petrophysical and chemical properties.

Microstructure of Zn-Al4 alloy microcastings by micro precision casting based on metal mold

Metal mold micron scale precision casting technology was developed successfully,and three-dimension complicated microgear castings in micron scale were produced.Evolvement regularity of microgear castings were observed by optical microscope and scanning electron microscope.Compared with conventional casting,microcasting is characterized by typical nonequilibrium solidification,for example,its grain size can be refined significantly,eutectic structure is transformed from lamellar morphology to rod eutectic,and the ratio of primary phase is increased.This kind of microstructure can promote mechanical properties of microcasting.

基于Micro-CT解析抗疏强骨方对去势小鼠骨微结构影响

目的运用Micro-CT断层扫描及三维重建技术探讨抗疏强骨方对去势雌性小鼠骨微结构的影响。方法清洁级6周龄KM雌性小鼠60只,根据分层随机法分为假手术组、模型组、阿仑膦酸钠组、抗疏强骨方组,除假手术组外,其余3组小鼠均手术切除双侧卵巢。术后1周开始灌胃给药,抗疏强骨方组和阿仑磷酸钠组除了分别每天23.53 g/kg抗疏强骨方和1.3 mg/kg阿仑膦酸钠灌胃,其他饲养方法与假手术组和模型组相同,连续治疗12周后处死取材。运用显微计算机断层扫描技术检测各组骨微结构;ELISA检测血清中骨特异性碱性磷酸酶(B-ALP)、骨钙素(BGP)、抗酒石酸酸性磷酸酶5b(TRACP-5b)含量。结果与假手术组比较,模型组小鼠骨小梁骨密度(Tb.BMD)、骨体积分数(BV/TV)、骨小梁数量(Tb.N)、骨小梁厚度(Tb.Th)降低(P<0.05),骨小梁分离度(Tb.Sp)、结构模型指数(SMI)增加(P<0.05);与模型组相比较,阿仑膦酸钠组与抗疏强骨方组中Tb.BMD、BV/TV、Tb.N、Tb.Th升高(P<0.05),Tb.Sp、SMI降低(P<0.05);从三维重建图看,模型组较假手术组股骨Ward三角区骨小梁数量稀疏、间隙变大;与模型组相比,阿仑膦酸钠组与抗疏强骨方组股骨近端股骨头内骨小梁相对完整;与假手术组比,模型组血清中B-ALP、BGP、TRACP-5b均升高(P<0.05);与模型组比,阿仑膦酸钠组与抗疏强骨方组血清中B-ALP、BGP、TRACP-5b降低(P<0.05)。结论抗疏强骨方可以减少去势小鼠骨量丢失,改善骨微结构,从而达到预防绝经后骨质疏松作用。

Microstructure and texture of electroformed copper liners of shaped charges

The microstructures of copper liners of shaped charges prepared byelectroforming technique were investigated by transmission electron microscopy (TEM). Meanwhile, theorientations distributing of the grains in the electroformed copper liners of shaped charges wasexamined by the electron backscattering Kikuchi pattern (EBSP) technique. TEM observations haverevealed that these electroformed copper liners of shaped charges have the grain size of about 1-3mu m and the grains have a preferential orientation distribution along the growth direction. EBSPanalysis has demonstrated that the as-formed copper liners of shaped charges exhibit amicro-texture, i.e. one type of fiber texture, and the preferred growth direction is normal to thesurface of the liners.

Effects of microrolling parameters on the microstructure and deformation behavior of pure copper

Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.