Investigations on optimal mode of electric explosion of conductors in water and air

In this work, it is established that the ratio of the stored energy to the conductor weight W ₀/m can be used as a similarity criterion for the electrical characteristics of conductor explosion. It is shown that the specific stored energy W ₀/m and the ratio of the sublimation energy of the conductor metal to the stored energy W _s /W ₀ for the optimal modes of electric explosion of conductors in air do not depend on externally driven parameters in the same way as for an explosion in water. The conditions providing a high rate of energy release in a discharge gap during EEC in air are determined. The relation between the optimal parameters of conductor explosion in water and air is found.     

Two body type abrasion wear behaviour in hypoeutectic 16%Cr cast irons with Mo

Abstract

Hypoeutectic 16%Cr cast irons, both Mo free and 1–3%Mo containing specimens were prepared to investigate their abrasion wear behaviour. Annealed specimens were hardened at 1323 K and then tempered at three temperatures from 673 to 873 K for 7·2 ks, the temperature giving the maximum hardness (H_Tmax) and the lower and higher temperature, (L-H_Tmax, H-H_Tmax). The abrasion wear behaviour was investigated using a two body type Suga abrasion wear tester. A linear relation was obtained between wear loss and wear distance. The highest wear resistance or the lowest wear rate (R _W) was obtained in H _Tmax specimens except for the Mo free specimen. The lowest wear resistance or the highest R _W was obtained in H-H_Tmax specimens. The R _W was decreased with an increase in macrohardness. The lowest R _W appeared around 25% retained austenite (V _γ ). The R _W was decreased with an increase of Mo content, and the V _γ value at the minimum R _W shifted to the high V _γ side.     

Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN

Ti-coated diamond with different particle sizes and proper amounts of cubic boron nitride (cBN) was used to fabricate polycrystalline diamond composite (PDC) with improved wear resistance and thermal stability under high temperature and high pressure (5.5–6.5GPa, 1500–1650 °C). The ratio of Ti-coated diamond powder, cBN powder and normal diamond powder was W_30–50: W_4–8: W_0–1 = 70: 15: 15. Cobalt (Co) was used as a binder, and cemented tungsten carbide was used as a substrate to sinter a new high-performance PDC. Ti and TiC on the surface of Ti-coated diamond reacted with cBN under high temperature and high pressure to generate new ceramic phases such as TiB₂, TiN and TiN_0.3, which have high hardness and good wear resistance. Compared with the conventional PDC, the impact toughness and wear resistance of PDC with Ti-coated diamond and cBN addition were enhanced by 19% and 28%, respectively. The ceramic phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperature to 942–950 °C, which were 162–170 °C higher than the conventional PDC. The new ceramic barrier wrapped around the surface of the diamond and Co after the formation of the D-D (diamond-diamond) bonding will give priority to the oxidation reaction of Co and diamond with oxygen, which prohibits cobalt-catalytic graphitization of diamond, meeting the needs of PDC thermal stability and wear resistance in the field of drilling.     

Microstructure and mechanical properties of SiC-nanowire-augmented tungsten composites

The effect of an addition of SiC nanowire on the microstructure and mechanical properties of tungsten-based composites is investigated in this study. SiC-nanowire-augmented tungsten composites were prepared by a spray-drying process and an in situ spark plasma sintering process. Three distinctive reaction phases, tungsten, tungsten carbide (W₂C) and rod-type tungsten silicide (W₅Si₃) were formed during the sintering process. The flexural strength was significantly increased from 706 MPa to 924 MPa in tungsten composites augmented with SiC nanowires, as was the formation of W₂C and W₅Si₃ phases. The rod-type W₅Si₃ bears significant stress by both sharing a portion of the load and providing a bridging mechanism. Furthermore, a high ablation resistance at an elevated temperature was observed for tungsten composites augmented with SiC nanowires.     

不同脉冲频率条件下2219-T87高强铝合金焊缝成形行为

采用复合超高频脉冲方波变极性钨极氩弧焊接技术完成了2219-T87高强铝合金平板堆焊试验,分析了脉冲电流频率对焊缝成形特征的影响及其规律.结果表明,脉冲电流频率对电弧特性及熔池流动行为有较大影响,造成焊缝熔宽、熔深及熔透率出现显著变化.脉冲频率f_H<60 kHz时,焊缝熔宽、熔深随脉冲频率的增加而增大,熔透率在f_H<35 kHz时基本保持不变,在f_H>35 kHz时出现显著提升,较常规变极性氩弧焊(VP-GTAW)至少提高了34%;当脉冲频率达到60 kHz时,焊缝熔透率达到最大,较VP-GTAW提高了约60%;脉冲频率f_H>65 kHz时,熔宽、熔深及熔透率呈现回落趋势.     

Influence of thickness on the material characteristics of reactively sputtered W2N layer and electrical properties of W/W2N/SiO2/Si capacitors

The material characteristics of W₂N layer and electrical properties of W/W₂N/SiO₂/Si metal–oxide–semiconductor (MOS) capacitors with different W₂N thickness upon annealing in N₂ + H₂ ambient at 500 °C for 20 min are investigated. The nitrogen concentration of W₂N for the W/W₂N stack with thin W₂N layer (≤10 nm) is lower than that for the W/W₂N stack with thick W₂N layer (≥15 nm). In addition, the crystallinity of W₂N in the W/W₂N (15 nm) stack is better than that in the W/W₂N (10 nm) stack. For all capacitors, the oxide charges decrease significantly after annealing and the amount of oxide charges is independent of the W₂N thickness. However, the work function (Φ_m) of the W/W₂N (≤10 nm) stack (4.6 eV) is smaller than that of W/W₂N (15 nm) stack (5.0 eV). The Φ_m of W/W₂N (15 nm) stack is close to that of W₂N single layer. After annealing, the Φ_m of W/W₂N (15 nm) stack and W₂N single layer decrease, especially for the W₂N single layer. But for the W/W₂N (≤10 nm) stack, the Φ_m increases after annealing.     

超细/纳米结构WC-10Co-4Cr涂层的透射电镜表征与性能分析

利用真空原位还原碳化反应合成超细/纳米WC-Co复合粉末,通过添加一定量Cr获得WC-10Co-4Cr复合粉末,经团聚造粒获得喷涂用复合粉末喂料,采用超音速火焰(HVOF)喷涂系统制备出超细/纳米结构的WC-10Co-4Cr涂层。利用X射线衍射仪,扫描电子显微镜和透射电子显微镜对涂层的物相、显微组织结构、元素分布特征等进行了系统表征,并对涂层耐磨性、耐蚀性进行了测试分析。结果表明:基于原位反应合成WC-Co复合粉制备的超细/纳米结构WC-10Co-4Cr涂层具有较好的耐磨性和耐腐蚀性。涂层以WC为主相,含有非晶结构的粘结相Co(Cr),同时存在少量六方晶体结构的W_2C相和非晶复相W_2C+Co(Cr)。对涂层中元素Co和Cr的分布进行了量化分析,得到其从WC晶粒到相界到共晶区再到Co区的变化规律。结合WC-10Co-4Cr复合粉末和超音速火焰喷涂工艺的特点,阐释了Cr在WC-10Co-4Cr涂层分布状态的形成原因,并讨论了对涂层性能的影响。     

Effects of pulsed and continuous Nd–YAG laser beam waves on welding of Inconel alloy

Abstract

In the present work a 2·5 kW high power Nd–YAG laser is used in the bead on plate (BOP) and butt welding of Inconel 690 plates of thickness 3 mm. Welding is performed using a rectangular laser pulse, for which the peak to base power ratio W_r is reduced from an initial value of 10 to a value of 1, maintaining an identical mean power of 1·7 kW. Therefore, the welding mode changes from a pulsed wave to a continuous wave. The BOP results indicate that the depth of the weld penetration increases at a lower travel speed and/or a higher value of W_r. In the butt welding process, as W_r is increased from 1 to 10, the cellular microstructure of the weld remains relatively unchanged, but the macroporosity formation ratio decreases from 7·1% to 0·6%. At low values of W_r, macroporosity is identified primarily in the root region. However, as W_r increases, the associated periodic high power increases the agitation of the molten pool and probably causes bubbles to float upwards. Consequently, at higher values of W_r, the regions of macroporosity are distributed randomly throughout the weld. Although microcracks are not apparent within any of the welds, each weld exhibits slight microporosity. This microporosity decreases as W_r increases. The present results confirm that a pulsed laser beam with an appropriate peak power can be used to achieve a compromise between the mechanical properties and surface roughness of the weld for Inconel 690 in Nd–YAG laser welding.     

铸钢轧辊电火花沉积WC-4Co涂层组织和性能分析

采用新型电火花沉积设备,把陶瓷WC-4Co电极材料沉积在铸钢轧辊材料上,制备了WC-4Co沉积涂层,研究了其微观组织及耐磨性能.结果表明,沉积层主要由Fe3W3C,Co3W3C,Fe和SiC等相组成;沉积层与基体呈冶金结合,过渡层组织主要是柱状晶结构组织;Fe3W3C和Co3W3C等硬质相弥散分布于沉积层Fe基体上,部分区域硬质相达到了纳米颗粒尺寸;沉积层硬度的平均硬度为1617.2HV;沉积层较铸钢轧辊的磨损性能提高了2.1倍,沉积层的磨损机理主要是粘着磨损、疲劳磨损、氧化磨损和磨粒磨损的综合作用,细小的弥散分布的硬质相是沉积层硬度及耐磨性提高的主要因素.     

TC4钛合金表面激光熔覆WC增强镍基复合涂层的组织及耐磨性

为提高TC4钛合金的耐磨性,利用激光熔覆技术(laser cladding,LC)在TC4钛合金表面制备Ni60+50%WC(体积分数)和deloro22(d22)粉末打底+(Ni60+50%WC)2种耐磨复合涂层。采用扫描电子显微镜(SEM)、能谱仪(EDS)以及X射线衍射仪(XRD)来表征涂层的微观结构和物相组成;使用HV-1000显微维氏硬度计、HRS-2M型高速往复摩擦磨损试验机和WDW-100D电子万能试验机来分析涂层的性能。结果表明:2种涂层均由W₂C、TiC、Ni₁₇W₃、Ni₃Ti和Ti_xW_1-x相组成,2种涂层不仅与基体呈现出优异的冶金结合,而且组织均匀致密,没有裂纹瑕疵;由于涂层中存在着原位合成的硬质相和细晶强化共同作用使得涂层硬度显著提高,约为TC4基体的2.82倍;2种涂层的摩擦系数(COF)和磨损量都远低于TC4钛合金基体;Ni60+50%WC复合涂层和d22粉末打底+(Ni60+50%WC)复合涂层的抗剪切结合强度分别为188....     

Micromechanical and microstructural properties of tungsten fibers in the as-produced and annealed state: Assessment of the potassium doping effect

Due to its high strength and low temperature ductility, tungsten fibers (W_f) have been widely used as reinforcement elements in metallic, ceramic and glass matrix composites to improve the strength, toughness and creep resistance. Materials designed for future fusion reactors also utilize the option of W_f reinforcement, i.a. with a copper (W_f/Cu) or tungsten (W_f/W) matrix. W_f/W composites are being intensively studied as risk-mitigation materials to replace bulk tungsten which is susceptible to embrittlement induced by neutrons resulting from fusion reaction. Operation of W_f/W in high temperatures (up to 1300 °C and even higher) fusion environment implies a risk of recrystallization and grain growth, which dimishes the attractive properties of tungsten fibers. In this work, we assess this modification of micro-mechanical and microstructural properties of tungsten fibers by means of nanoindentation, scanning electron microscopy, electron back-scattering diffraction analysis and corelate it with the ultimate tensile strength and fracture modes observed in the tensile tests. Both pure W and pottasium doped wires in the as-fabricated and annealed states are investigated and the results are compared with bulk tungsten, also exposed to several annealing temperatures. The results highlight the postive impact of potassium doping which shifts the threshold temperature for the grain growth by about 600 °C compared to pure tungsten wire. The results of the nanoindentation revealed systematic linear correlation with the ultimate tensile strength, which therefore offers a complimenatary way of micro-mechanical testing linking it with macro-scale properties of the wires.     

Structure and oxidation resistance of W1–xAlxN composite films

A series of W_1–xAl_xN films (0<x<38.6%, mole fraction) were deposited by reactive magnetron sputtering. The composition, microstructure, mechanical properties and oxidation resistance of the films were characterized by EPMA, XRD, XPS, nano-indentation, SEM and HRTEM. The effect of Al content on the microstructure and oxidation resistance of W_1–xAl_xN films was investigated. The results show that WN film has a face-centered cubic structure. The preferred orientation changes from (111) to (200). The W_1–xAl_xN films consist of a mixture of face-centered cubic W(Al)N and hexagonal wurtzite structure AlN phases. The hardness of the W_1–xAl_xN films first increases and then decreases with the Al content increasing. The maximum hardness is 36 GPa, which is obtained at 32.4% Al (mole fraction). Compared with WN film, the W_1-xAl_xN composite films show much better oxidation resistance because of the formation of dense Al₂O₃ oxide layer on the surface.     

Microstructure, mechanical and tribological properties of CrN/W2N multilayer films deposited by DC magnetron sputtering

CrN/W₂N multilayer films with various bilayer periods of 15-85 nm were deposited on high speed steel (W18Cr4V) substrates by means of DC closed field unbalanced magnetron sputtering. The morphology and microstructure of the multilayer films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The mechanical and tribological properties were evaluated using a nanoindentor, Rockwell and scratch tests and a conventional ball-on-disk tribometer, respectively. There were some transverse grains at the layer interface and the interface between the CrN and W₂N layers was not so sharp owing to atom diffusion through the interface. In the bilayer period range, the microhardness, elastic modulus and adhesive strength of the CrN/W₂N multilayer films increased with the decrease of bilayer period. The CrN/W₂N multilayer film with a bilayer period of 15 nm showed the highest hardness (29.2 GPa), elastic modulus (376 GPa) and best adhesion strength, it also had the highest wear resistance and lowest friction coefficient.     

Apparent Activation Energy of the Anodic Dissolution of Nickel in Sulfuric Acid Solutions in the Presence of Cl– and CNS– Ions

Apparent activation energies W of the anodic dissolution of nickel in 0.5 M H₂SO₄ are determined with the use of temperature-kinetic method at certain assumptions in a wide range of potential values E. The effect of the nature of anion-activator on the character of the W = f(E) dependence is revealed. The data obtained are interpreted in terms of the concept of hard and soft acids and bases.     

Penetration in spot GTA welds during centrifugation

Convective flow during arc welding processes mainly depends on electromagnetic force, Marangoni force, and buoyancy force. The Marangoni flow (caused by surface tension gradient,dγ/dT)and the buoyancy driven flow are the major factors in controlling weld penetration in austenitic stainless steels, such as types 304 and 316. Alloys 304 and 316 were subjected to a 7 s spot gas-tungsten arc (SGTA) welding at 1 g (g = 9.8 m/s ² )and 5 g accelerations. The welds at 5 g were performed on Clarkson University’s multigravity research welding system (MGRWS). The cross sections of the fusion zones were polished/etched, and their depth (D)and width (W)were measured to ± 0.025 mm. It was determined that the depth/width ratio (D/W)of the welds decreased as the acceleration increased from 1 to 5 g. This result indicates that increase in buoyancy driven flow will produce wider but shallower welds during SGTA welding.     

Q235钢表面激光熔注WC涂层的微观组织及耐磨性

采用激光熔注技术对材料进行表面强化具有显著的优点.将WC陶瓷作为注入颗粒,在Q235钢表面制备激光熔注层.对激光熔注工艺进行了系统研究.利用SEM,EDS,XRD等手段分析熔注层的微观组织结构,对熔注层的硬度和耐磨性能进行了测试.结果表明,成功的激光熔注过程需要严格的工艺参数条件,采用优化的工艺参数时激光熔注WC表面层成形良好.熔注层主要由WC,W2C以及M6C(Fe3W3C-Fe4W2C)强化相组成,Fe3W3C分别以颗粒之间基体上的树枝晶和依附WC颗粒形成的反应层两种形态存在于熔注层中;熔注层平均硬度约为母材硬度的4倍,熔注层摩擦系数不超过基体的1/4,熔注层耐磨性良好.     

激光热喷涂Co30Cr8W1.6C3Ni1.4Si涂层在PAO+2.5%MoDTC油中摩擦学特性

为了提高TC4合金的耐磨性能,采用激光热喷涂技术在其表面制备了Co₃₀Cr₈W_1.6C₃Ni_1.4Si涂层。通过扫描电子显微镜（SEM）和X射线衍射（XRD）分析了涂层的形貌和物相,并通过摩擦磨损实验研究了涂层在PAO+2.5% MoDTC（质量分数）油中的磨损行为。结果表明,激光热喷涂的Co₃₀Cr₈W_1.6C₃Ni_1.4Si涂层主要由Ti、WC_1-x、CoO、Co₂Ti₄O和CoAl相组成,在涂层界面形成冶金结合。在激光功率为1000、1200和1400 W时所制备的涂层平均摩擦因数分别为0.151、0.120和0.171,其对应的磨损率分别为1.17×10^-6、1.33×10^-6和2.80×10^-6 mm³?N^-1?m^-1,磨损机理为磨粒磨损,其枝晶尺寸对降磨起主要作用。     

Clarification of chemical state for alloying elements in iron rust using a binary-phase potential-pH diagram and physical analyses

A binary-phase potential-pH diagram has been investigated to evaluate the chemical stability of various kinds of double oxide rusts (Fe-X) to get a principle for alloy design enhancing the corrosion resistance of steels. It was found that there are the following types of alloying elements enhancing the corrosion resistance of steels in the rust: (1) iron substitution type (Ni), (2) oxide formation type (Al), (3) metallic type (Ru), and (4) oxygen-acid salt type (WO₄). X-ray photoelectron spectroscopy and transmission electron microscopy analyses have been conducted on the rust formed on the low alloy steel in a saline environment. The analytical results were discussed using potential-pH diagrams. The iron substitution type and the oxide formation type elements make spinel double oxides with iron. In the corrosion tests, steels added with Ni or Al had high corrosion resistance. Thus it is possible to obtain high corrosion resistance by the creation of spinel double oxide such as Fe₂NiO₄ and FeAl₂O₄ in an inner layer.On the other hand it was found that the metallic type and the oxygen-acid salt type elements were not contained into the iron rust. In particular the oxygen-acid salt elements were excluded from the iron rust and concentrated into the defects of the rust. It is suggested that insoluble salts like FeWO₄ are formed on the base metal in the defects to act as an anodic inhibitor. Thus, the addition of a small quantity of W gives high corrosion resistance.The penetration of Cl ions can be prevented by the spinel double oxide in an inner layer and the oxygen-acid salt in the defects. In this way, the high corrosion resistance by the addition of these elements can be understood from the potential-pH diagram and the physical analyses.     

High-temperature tribological behaviors of Ti2AlNb-based alloys by plasma surface duplex treatment

Plasma tungstening followed by carburization (W-C duplex treatment) was performed on the Ti₂AlNb-based (O phase) alloy by using the double glow plasma process to enhance its wear resistance. The microstructure and high-temperature tribological behaviors of the un-treated and W-C duplex-treated samples were investigated. The results show that the duplex-treated layer is mainly composed of W₂C or W₆C_2.54 phases and the contents of W and C elements in the alloyed layer change gradually along the depth by surface plasma duplex treatment. The diffusion depth of W is about 12 μm, while the carbon atoms most exist in the depth more than 12 μm. High temperature tribometer tests indicate that the friction coefficient of the W-C duplex-treated layer is approximately 1/6 that of substrate. The wear rate of the duplex-treated layer is about 28% that of the untreated one. So, plasma surface W-C duplex treatment can obviously improve the high-temperature tribological resistance of Ti₂AlNb-based alloy. The tribological mechanism of the duplex-treated layer is discussed by dividing the friction process of the duplex-treated layer into three fluctuate stages. The first stage is the formation of oxide film between W-C duplex-treated layer and counterface. The second stage is the detachment of oxide film, acting as “the third body”. The last stage is the period that the friction and wear occur between the compact particle layer and counterface.     

Improved Hardfacing for Drill Bits and Drilling Tools

New flame spray hardfacing, DSH (DuraShell^® Steel Hardfacing, US patent pending), was developed to improve thermal conductivity, abrasion wear, and erosion resistance for subterranean drilling application. The materials consisted of spherical cast WC/W₂C and Ni-Si-B alloy powders. The hardfacing compositions were tailored for various processes such as flame spray and laser cladding. Typically, the hardfacing comprised hard tungsten carbide particles being uniformly distributed in a tough Ni-alloy matrix. The hardness of WC/W₂C exceeded 2300 Hv_.3 and that of Ni-alloy matrix varied from about 400 to 700 Hv_.3. High- and low-stress abrasion resistances of these hardfacing materials were characterized and compared to the conventional hard coatings of cast WC/W₂C and Ni-Cr-Si-B-Fe. The increase in thermal, wear, and erosion resistances of the hardfacing improved the durability of PDC (polycrystalline diamond compact) steel body bit and drilling tools and their cost-effective performance. Several case studies of DSH hardfacings on drill bits were described.