Fine Columnar Grains Research Articles

고분자전해질 연료전지용 바이폴라 플레이트의 표면형상과 전기적 특성

The multi-films of a metallic film and a transparent conducting oxide (TCO, indium-tin oxide, ITO) film were formed on the stainless steel 316 and 304 plates by a sputtering method and an E-beam method and then the external metallic region of the stainless steel bipolar plates was converted into the metal nitride films through an annealing process. The multi-film formed on the stainless steel bipolar plates showed the XRD patterns of the typical indium-tin oxide, the metallic phase and the metal substrate and the external nitride film. The XRD pattern of the thin film on the bipolar plates modified showed two metal nitride phases of CrN and Cr₂N compound. Surface microstructural morphology of the multi-film deposited bipolar plates was observed by AFM and FE-SEM. The metal nitride film formed on the stainless steel bipolar plates represented a microstructural morphology of fine columnar grains with 10 ㎚ diameter and 60㎚ length in FE-SEM images. The electrical resistivity of the stainless steel bipolar plates modified was evaluated.

Characterization of texture and microstructure of electrodeposited Ni layers

AbstractThe texture and microstructure of electrodeposited Ni layers formed in an additive-free Watt's bath were investigated. The microstructure of the electrodeposited Ni layer consists of fine columnar grains extending along the growth direction. The major texture components of electrodeposited Ni layers on Ni-P substrate were (112) and (110) fibers. On the other hand, electrodeposited Ni layers on Cu substrate had a strong (110) fiber texture. In the vicinity of the interface between the electrodeposited Ni layer and the Cu substrate, obvious epitaxial regions were not observed. Many twins parallel to the growth direction were observed in the electrodeposited Ni layer. It is suggested that grains with a twin relationship grew preferentially during the electrodeposition reaction.

1201 めっき銅薄膜の疲労強度特性の熱履歴依存性(S05-1 ナノ・マイクロ材料の強度・信頼性(1)銅薄膜の強度物性,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Effect of heat treatment on the fatigue strength of electroplated copper thin films was investigated. Test electroplated copper films were grown on stainless steel substrates by using acid copper sulfate bath without any additive agent. These films were annealed at 400℃ for 3 hours in argon atmosphere. Mechanical properties of annealed film were similar to that of bulk material because the grain size of the films was increased by annealing. It was also found that the fracture mode of the annealed films changed drastically. The annealed film showed ductile fracture though the initial film without annealing showed brittle fracture. The high cycle fatigue strength of the as-electroplated films was lower than that of the annealed films. This was because that the micro structure of the film consisted of fine columnar grains with weak grain boundaries.

A study of direct- and pulse-current chromium electroplating on rotating cylinder electrode (RCE)

Direct- and pulse-current (DC and PC) chromium electroplating on Cr–Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50°C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60Adm−2, respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit.

Epitaxial Grain Growth during Surface Modification of Friction Stir Welded Aerospace Alloys by a Pulsed Laser System

The liquid film re-growth behaviour resulting from pulsed laser surface melting (LSM) has been investigated for typical 2xxx, and 7xxx aerospace alloys, both on parent plate and friction stir welded (FSW) joints. In Zr free alloys, as a result of the high growth rate and steep thermal gradient, the melted layer re-grew with a stable front, epitaxially, from the parent subsurface grains. This caused a thin coarse grained solidified layer to form over the parent material, thermomechanically affected zone (TMAZ) and heat affected zone (HAZ), and fine columnar grains to develop over the FSW nugget zone of the same order in width as the nugget grain size. In the case of the Zr containing alloys, a very fine columnar grain structure was found over the entire surface, independent of the subsurface grain structure. This has been shown to occur by growth selection from a band of nanoscale Al grains epitaxially nucleated on Al3Zr dispersoids, at the melt solid interface, that had not fully dissolved in the melt.

Microstructure change and shape memory characteristics in welded Fe–28Mn–6Si–5Cr–0.53Nb–0.06C alloy

In the present study, an Fe–28Mn–6Si–5Cr–0.53Nb–0.06C (mass%) alloy was employed to investigate the influence of laser beam welding (LBW), electron beam welding (EBW) and tungsten-insert gas welding (TIGW) on shape memory properties. This alloy was recently found to exhibit very good shape memory effect with simple thermomechanical treatments without so-called the ‘training’. After homogenizing heating at 1470 K for 10 h, two different treatments were performed: (a) 14% rolled at 870 K followed by aging at 1070 K for 10 min and then welded, (b) first welded and then extended 10% at room temperature, followed by aging at 1070 K for 10 min. The results show that the shape recovery of the alloy was slightly different depending on welding method. The shape recoveries for the samples treated in (a) by LBW, EBW and TIGW were 90%, 87%, 81% and those for the samples treated in (b) were 86%, 84% and 79%, respectively. After welding, the alloy still possesses very high shape recovery stress of about 250 MPa for the samples treated in (a). High strength of the weld zone is due to the dendrite structure with very fine columnar grains. All of these results on welding will make a wide industry application of the Fe–Mn–Si based SMAs in the near future.

Effect of Al content on the properties of Cr 1− xAl xC films prepared by RF reactive magnetron sputtering

Cr 1− x Al x C films were deposited on high-speed steel by RF reactive magnetron sputtering. In this study, we aimed to identify the effect of the Al content on the properties of Cr 1− x Al x C films. We found that Cr 1− x Al x C films exhibited a fine columnar grain microstructure with some special characteristics, such as high hardness of Hv 1426, a low friction coefficient of 0.29, and a large contact angle of 90° for x = 0.18. Furthermore, an increase in Al content resulted in a decrease in film hardness and an increase in contact angle. Moreover, on annealing at 923 K, the mechanical properties of the films improved and a dense protective film of complex Cr 2O 3 and Al 2O 3 oxides was formed on the surface for better wear resistance, which will ultimately increase the lifetime of the high-speed steel substrate.

Grain alignment and microstructure of (Nd,Dy)12.8(Fe,M) 80.7B6.5 by strip casting

The alignment of Nd2Fe14B grains (T1) and the microstructure of (Nd,Dy)12.8(Fe,M) 80.7B6.5 strip cast ribbons are reported in this paper. In the strips there is a pronounced texture of the tetragonal T1 phase and the columnar grains exhibit apparent alignment along [00L]. The alignment coefficient ϕ changes with the wheel speed V and is highest at V=1.5–2m/s. The Nd-rich phase is well segregated and widely distributed enclosing the fine columnar grains of the main phase in the strips prepared at V=2m/s. The magnetic properties of sintered magnets prepared from this kind of (Nd,Dy)12.8(Fe,M) 80.7B6.5 strip cast ribbons are as follows: Br=1.457T(14.57kG), Hcj=1048kA/m (BH)max=408kJ/m3 (51.3MGOe).

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 20 CrMo 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 M23 C6 (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.

Influence of Pt/TiO2 Bottom Electrodes on the Properties of Ferroelectric Pb(Zr,Ti)O3 Thin Films

Pb(Zr,Ti)O3 (PZT) thin films were deposited onto Pt/TiO2/SiO2/Si substrates with different-types of TiO2 layers by liquid delivery MOCVD at 550°C. Three kinds of TiO2 adhesion layers were examined: 200 oriented TiO2 with rutile structure, 103 oriented TiO2 with anatase structure and randomly oriented TiO2 which consisted of nanocrystals. In the anatase case, the PZT thin film consisted of large tetrapod-like grains with 111 orientation while the PZT film had a 001/100 mixed orientation and consisted of fine columnar grains in the rutile cases. In the nanocrystal case, the orientation was weak and the film consisted of both types of grains. From these results, we concluded that highly oriented TiO2 formed at higher temperature, the rutile TiO2 in this investigation, is the better material for the under layer. However, the remanent polarization of the PZT capacitor with the rutile TiO2 significantly increased with polarization reversal because the PZT film had a 001/100 mixed orientation. Some seeding layer will be required to obtain 111 oriented PZT thin films on Pt/TiO2/SiO2/Si substrates with rutile TiO2.

F07-(3) スマート化への材料・デバイス研究

High performance and multi-functional sensor/actuator materials is essential key technology developing smart/intelligent devices and systems. Fine fiber and foil-type sensor/actuator material elements of thermoslastic, ferromagnetic and magnetoelastic alloys were developed by using the originally designet rapid solidification (RS) melt-spinning apparatus. Those RS had strong crystalline texture with fine columnar grains that were uniquely formed during rapid-solidification process. These sensor/actuator material elements become useful to develop the high performance micro-electronic mechanical systems and intelligent/smart composite materials and structures. Several potential designs for faster composite actuator, medical catheter gripper and smart composites board for structural health-monitoring are shown as preliminary application proposals based on this study.

746 急冷凝固感温型形状記憶合金の温度特性マップ (SMA-MAP)

Material Characteristics of thermoelastic shape memory alloy(SMA) have to be improved toward two times higher level so that SMAs can be applied to smart material/structure systems. For this purpose, the novel material processing technique, "Rapid-solidification, melt-spinning method" was used to control the crystal microstructures with fine columnar grains with strong texture. We succeeded in producing the rapid-solidified various kinds of SMA (TiNiCu, TiNiPd, NiAlMn, RuNb, RuTa systems) foils and fine fibers with sharper hysteresis and more ductility than those of bulk-materials. The thermo-mechanical properties of these SMAs were investigated systematically. Next, SMA bulk actuator material to get large recover force could be produced by adopting short time spark plasma sintering (SPS) method for rapid-solidified SMAs ribbons/fibers. Lastly, new concept for complex thermo-magneto actuator with capability of more rapid response speed was proposed. That was designed by combination super-elastic character of SMA with bias-magnetic force. These results are useful for develop the smarter materials and structure systems based on SMA technology.

Effect of Interface Wetting on Flattening of Freely Fallen Metal Droplet onto Flat Substrate Surface

A free-falling experiment was conducted as a simulation of a thermal spray process. The flattening behavior of the freely fallen metal droplet impinged onto a flat substrate surface was investigated in a fundamental way. The substrates were kept at various temperatures, and the substrates were coated with gold by physical vapor deposition (PVD) and were prepared in order to investigate the effect of wetting at the splat-substrate interface on the flattening behavior of the droplet. A falling atmosphere was created with atmospheric pressure of nitrogen to prevent the oxidation of the melted droplet. Experiments under low-pressure conditions also were conducted. The different types of splat morphology were recognized in experiments conducted under a nitrogen atmosphere with atmospheric pressure. The splat morphology on a substrate at room temperature was of the splash type, whereas that on a substrate at high temperature was of the disk type. The microstructure observed on a cross-section of the splat obtained on the substrate at room temperature was an isotropic coarse grain, whereas that on the substrate at high temperature was a fine columnar grain. The grain size changed transitionally with increasing substrate temperature. The temperature of the transition on the gold-coated substrate was higher than that on the naked substrate. The microstructure of the cross-section of the splat obtained under low pressure was finely columnar even on the substrate at room temperature. The results indicate that the metal droplet wets better under the low-pressure condition than under the atmospheric pressure nitrogen condition and that wetting has a significant role in the flattening of the droplet.

Li 3Sc 2− xFe x(PO 4) 3 thin films and powders prepared by ultrasonic spray pyrolysis

Thin films of Li 3Sc 2− x Fe x (PO 4) 3 ( x=0.5, 2) solid electrolytes have been prepared on quartz glass substrates by ultrasonic spray pyrolysis (USP) using aqueous solutions of LiH 2PO 4, Sc(NO 3) 3 and Fe(NO 3) 3 at substrate temperature of 500–700°C. The amorphous as-deposited films were converted into crystalline materials by heat treatment at 800–1000°C. The optimal deposition parameters for formation of uniform precursor films with good adhesion to the substrate were determined. The dense films composed of fine columnar grains were obtained using the three cycles of deposition and annealing. The room temperature ionic conductivity of the film with the composition x=0.5 was 5×10 −6 S/cm. The superionic γ-phase of USP ceramics of Li 3Sc 2− x Fe x (PO 4) 3 (0< x≤0.6) was shown to be stabilized at room temperature, which may be caused by slight structural distortions and changes in the interactions between the lithium ions during Sc 3+→Fe 3+ substitution. The highest ionic conductivity σ(25°C)≈1×10 −5 S/cm was observed for ceramics with x=0.4.

Low-Temperature Crystallization of Sol-Gel Derived Pb(Zr0.4,Ti0.6)O3 Thin Films

We have studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 435 down to 420°C. The PZT(40/60) films were prepared at these temperatures on Pt/SiO2/Si substrates by a combination of diol-based solutions and modified film preparation processes. Various properties of the PZT(40/60) films such as microstructures, crystal orientation, ferroelectric properties, relative permittivity, and leakage current density were evaluated. It was found that PZT(40/60) films could be crystallized at 435 to 420°C by the diol-based solutions and the modified film preparation processes. The PZT(40/60) films had microstructures with perovskite-single-phase fine columnar grains and good electric characteristics such as remanent polarization (Pr) of 12 to 15 µC/cm2, relative permittivity (εr) of 780, and breakdown voltage of more than 10 V.

Keimbildung und Schicht-Wachstum beim Titanieren von Schnellarbeitsstahl / Nucleation and Coating Growth in the Titanising of High Speed Steels

In order to increase their resistance to wear and corrosion, high speed steels are often hard faced with titanium based coatings. In the work discussed in this article, such coatings are produced by a process of thermo-chemical diffusion known as titanising. The nucleation and growth mechanisms of the coatings produced using this process are investigated. In the investigation the process parameters of coating time and temperature are varied, and the titanium carbide coatings produced examined and characterised in respect of their morphology, chemical composition and crystallographic structure. The nucleation and growth of the coatings are affected by each of the two components of the substrate, these being the primary carbides and the matrix containing dissolved carbon. The formation of the coating starts with the matrix on which the nuclei form, which then proceed to cover the whole of the surface of the metal by a process of lateral growth. The temperature of the process has a considerable effect on both the nucleation process and growth of the coating, an increase in the processing temperature resulting in a reduction in the nucleation density. The coatings exhibit a morphology made up of fine columnar crystals and grains. The chemical composition of the coatings is largely dependent on the parameters investigated. With short treatment times Ti(C,N)-coatings are obtained, whilst with longer coating times combined with higher process temperatures, TiC-coatings are formed.

Low-pressure plasma-sprayed ZrO 2–CaF 2 composite coating for high temperature tribological applications

The microstructure and tribological behavior of low-pressure plasma-sprayed (LPPS) ZrO 2–CaF 2 composite coatings were studied. Optimum spray parameters were obtained to produce a less porous and strongly adherent ZrO 2–CaF 2 composite through carefully selecting the powder feed rate, primary gas pressure and spraying distance. The as-sprayed composite coating exhibited a typical lamellar structure of ZrO 2 and CaF 2 constituents, with a lot of microcracks in the splats. The resolidified interfacial structure featured by fine columnar grains were observed at the boundaries of ZrO 2 lamellae and were considered to have formed due to the local temperature and compositional variations during the solidification process of the molten splats. Small amounts of discontinuous oxides distributed at the interface region between the coating and substrate were demonstrated to be a mixture of the complicated oxidized products of iron, chromium, nickel and calcium, ZrO 2(Y 2O 3) particles, and independent Al 2O 3 and SiO 2 particles located within the rough surface of the substrate. The ZrO 2–CaF 2 composite surface exhibited a distinct improvement in wear resistance and frictional characteristics in comparison to Y 2O 3-stabilized ZrO 2 (YPSZ) coating at elevated temperatures. At 600 and 700°C, the composite exhibited a lower friction and wear than at room temperature, 400 and 800°C. CaF 2, acting as a solid lubricant at 600°C, effectively reduces friction and wear. Different tribological behaviors were observed on the worn surfaces, with different microstructural features after the 600°C wear test. In the individual ZrO 2 splats, microcracking and microfracture dropping led to material removal. However, in CaF 2 splats smooth CaF 2 surface films containing fine ZrO 2 hard particles was formed to reduce the friction and wear. Brittle fracture and delamination of ZrO 2–CaF 2 composite were demonstrated to be the dominant wear mechanisms at room temperature and 400°C. Plastic deformation, the continuous formation of CaF 2 transfer films, adhesive wear and viscous flow appeared as the dominant wear mechanisms at the higher temperature used in this investigation.

Growth of yttria stabilized zirconia thin films by metallo-organic, ultrasonic spray pyrolysis

Randomly and preferentially oriented thin films of yttria stabilized zirconia (YSZ) have been prepared on fused quartz substrates by ultrasonic spray pyrolysis using zirconium octylate and yttrium octylate as metallo-organic precursors at a substrate temperature of 873–1023 K. The as-deposited films composed of fine columnar grains were found to be crystalline and transparent with a cubic fluorite structure. With increasing substrate temperature the growth rate and diameter of the columnar grains increased and the crystal habit showed a preferential orientation at the (111) plane.

Thickness dependent mechanical behavior of submicron aluminum films

Mechanical behavior of thin metallic films has been investigated on aluminum films deposited on a flexible polyimide substrate. Aluminum thin films exhibit a higher tensile strength than bulk aluminum. As film thickness decreases from 480 to 60 nm tensile strength increases from 196 to 408 MPa. These mechanical behaviors are correlated with the microstructure and its evolution with the thickness of aluminum thin films. Films are consisted of fine columnar grains and average grain size increases monotonically with the film thickness. The volume fraction of (111)-textured grains increases and the dispersion of texture axis becomes narrow as the film thickens. The relative contributions of the film thickness, grain size, and texture to the strength of aluminum thin films are estimated using an empirical strengthening model. The result indicates that the high strength of aluminum thin films is due largely to their small grain size, followed by the strengthening due to the film thickness and texture.

LASER METAL FORMING: PROCESS FUNDAMENTALS

Laser metal fornling (LMF) is an innovative application for lasers with industrial potential for small series production, rapid prototyping, or repair engineering. It consists in the production of full strength metallic engineering components using a three-dimensional laser cladding process. Prototypes produced by LMF can be used to test the performance and reliability aspects of a particular design and must therefore have physical and mechanical properties similar to those of the mass produced part. The LMF technique can also be used to repair metallic parts and improve their life cycle behaviour. The fundamental aspects of this free forming technique were investigated to contribute to the physical understanding and to better control of the process. To this end, only simple geometrical parts have been produced. It was found that the dimensions, the shape, the shape instabilities, and the surface quality of the final components depend on the melt dynamics and on the kinetics of oxide formation at the surface of the alloy. Process conditions leading to the production of high quality parts have been determined for materials including steels, Stellite 6, IN 625 superalloy, and tin. The parts produced exhibit microstructures consisting of fine columnar dendritic grains without porosity and with mechanical properties equal to those of cast material.