The synthesis of bulk material through explosive compaction for making intermetallic compound Ti5Si3 and its composites

The possibility of synthesizing Ti₅Si₃ from mixed elemental powders and the fabrication of its composites by explosive compaction is discussed. A new technique using underwater shock waves was developed and it was found to exercise better control over the influencing parameters. Two processes were employed viz., (1) direct shock-induced reaction and (2) explosive compaction followed by heat treatment. The methodology to produce bulk material by the above two processes are reported. Ti₅Si₃ intermetallic synthesized by the two processes reveals high hardness than commercially available Ti₅Si₃.     

Synthesis of Ti-based bulk quasicrystal by shock compression

We attempted to produce a Ti₄₅Zr₃₈Ni₁₇ bulk icosahedral (i) quasicrystal by a shock compression technique, in which a single-stage powder gun discharges a flyer plate that consolidates the target powders. The results were also compared with those by a conventional hot-pressing. The powder mixtures for the shock compression were blended by two kinds of methods; that is, gently mixing in a vial, and mechanically alloying by a planetary ball mill. A large bulk i-phase sample, with a Ti₂Ni crystal phase, was synthesized from mechanically alloyed powders after shock compression at a higher flyer velocity, although the conventional hot-pressing at 3 MPa synthesized only the Ti₂Ni phase. For the gently mixed powders, no reaction occured even after shock compression. High-pressure and high-temperature produced during shock compression, and milling process were key factors to obtain the i-phase. The Vickers hardness and the wetting contact angle with pure water under an atmospheric pressure for the bulk sample containing the i-phase were about 7 GPa and about 70°, respectively.     

Explosive shock loading of alpha-Si3N4 powder

Alpha-Si₃N₄ powders were explosively shock loaded at levels of 260 and 570 kbar pressure. Specimens exhibited densification without additives into the 93 to 98% dense range as a result of shock-induced consolidation. X-ray line broadening investigations indicated that significant residual, internal strain levels of the order of 0.4% were developed in the densified material. Hardness and indentation fracture toughness values for shock-densified regions were nearly equivalent to those for ultra-high-pressure hot-pressed Si₃N₄ without densification aids.     

Dynamic consolidation of rapidly solidified titanium alloy powders by explosives

Consolidation of rapidly solidified titanium alloy powders employing explosively generated shock pressures was carried out successfully. The cylindrical explosive consolidation technique was utilized, and compacts with densities in the range 97 to 100% were produced. Better consolidation (with more interparticle melting regions and less cracking) was achieved by using a double tube design in which the outer tube (flyer tube) was explosively accelerated, impacting the powder container. Optical and transmission electron microscopy observations were carried out to establish microstructural properties of the products. It was observed that consolidation is achieved by interparticle melting occurring during the process. The interior of the particles in Ti-17 alloy exhibited planar arrays of dislocations and twin-like features characteristic of shock loading. Two dominant types of microstructures (lath and equiaxed) were observed both in Ti-662 and Ti-6242 + 1% Er compacts, and very fine erbia (Er₂O₃) particles were seen in the latter alloy. The micro-indentation hardness of the consolidated products was found to be higher than that of the as-received powder material; and the yield and ultimate tensile strengths were found to be approximately the same as in the as-cast and forged conditions. The ductilities (as measured by the total elongation) of the shockcompacted materials were much lower than those of the cast or forged alloys. Hot isostatic pressing of the shock-consolidated alloys increased their ductility. This enhancement in ductility is thought to be due to the closure of existing cracks. These excellent mechanical properties are a consequence of strong interparticle bonding between individual powder particles. It was also established that scaling up the powder compacts in size is possible and compacts with 50, 75, and 100 mm diameter were successfully produced.     

Shock-induced transformations of andalusite and kyanite powders

Exposure of andalusite and kyanite powders (40 m) to high dynamic pressures revealed a strongly different behaviour of the two materials against shock. While experiments on andalusite powders yielded characteristic shock-induced phase transformations, kyanite powders did not show any phase change upon release from shock compression. X-ray patterns and infra-red spectra proved the formation of 3/2-mullite from andalusite, and infra-red spectra also indicated the formation of long-range-disordered Al₂O₃ and SiO₂. While the formation of mullite must be associated with high (shock) temperatures, the formation of the Al₂O₃ + SiO₂ oxide mixture may be a (shock) pressure effect. The lack of temperature-induced transformations in kyanite may be explained by the lower porosity of the sample tablets as compared to those of andalusite. The absence of highpressure transformations in kyanite is most probably due to its dense structure which is more resistant to shock waves than the more open andalusite structure.     

Research on explosive welding of aluminum alloy to steel with dovetail grooves

In order to explore a new method for the explosive welding of aluminum alloy to steel, a 5083 aluminum alloy plate and a Q345 steel plate with dovetail grooves were respectively employed as the flyer and base plates. The parameters adopted in the explosive welding experiment were close to the lower limit of weldable window of 5083 aluminum alloy to Q345 steel. The bonding properties of 5083/Q345 clad plate were studied through mechanical performance tests and microstructure observations. The results showed that the aluminum alloy and steel plates were welded under the actions of metallurgical bonding and meshing of dovetail grooves. The tensile shear strength of 5083/Q345 clad plate met the requirements of the bonding strength of Al/Fe clad plate. The interfaces between aluminum alloy and the upper and lower surfaces of dovetail grooves were mainly welded through direct bonding, and discontinuous molten zone emerged in the local region; while the interface between aluminum alloy and the inclined surface of dovetail grooves was bonded by continuous molten layer. The brittle intermetallic compounds FeAl₂ and Al₅Fe₂ were generated at the bonding interfaces of 5083/Q345 clad plate. The fracture surface of the tensile specimen exhibited ductile and quasi-cleavage fractures.     

Study of collapse of a free surface conical cavity due to a plane or spherical shock wave

A plane faced or spherical target, having a central conical cavity at one face, has been subjected to plane or spherical shock loading at its other face by contact explosive or the impact of a flyer plate. The shock wave generated in the target interacts with the cavity and as a consequence the cavity collapses and a high velocity metal jet is produced. Target free surface velocity, shock wave velocity and jet velocity were measured using high speed oscilloscopes. The results revealed that the jet velocity is linearly related to the shock-induced particle velocity in the target. Considering it to be sink-type incompressible flow, a semiempirical analysis of the collapse has been presented which agrees well with the experiments.     

Explosive shock-compression processing of titanium aluminide/titanium diboride composites

Explosive shock-compression processing is used to fabricate Ti₃Al and TiAl composites reinforced with TiB₂. The reinforcement ceramic phase is either added as TiB₂ particulates or as an elemental mixture of Ti + B or both TiB₂ + Ti + B. In the case of fine TiB₂ particulates added to TiAl and Ti₃Al powders, the shock energy is localized at the fine particles, which undergo extensive plastic deformation thereby assisting in bonding the coarse aluminide powders. With the addition of elemental titanium and boron powder mixtures, the passage of the shock wave triggers an exothermic combustion reaction between titanium and boron. The resulting ceramic-based reaction product provides a chemically compatible binder phase, and the heat generated assists in the consolidation process. In these composites the reinforcement phase has a microhardness value significantly greater than that of the intermetallic matrix. Furthermore, no obvious interface reaction is observed between the intermetallic matrix and the ceramic reinforcement.     

NiAl-Al2O3 intermetallic matrix composite prepared by reactive milling and consolidation of powders

Reactive milling of nickel oxide and aluminium powders corresponding to the stoichiometric reaction 3NiO + 5Al resulted in the formation of intermetallic matrix composite NiAl-Al₂O₃, with 28 wt% of alumina. Prolongation of the milling process allowed obtaining the microstructure with nanosize range of crystallites of both phases, as showed XRD measurements and TEM observations. The refinement of microstructure was accompanied with an increase of lattice strain as a result of ball milling. The particles size and morphology changed from several tens of micrometers and polyhedron shape observed immediately after the reaction took place, to several micrometers and spherulitic shape after long-term milling. Two consolidation techniques of nanocomposite powders were applied: explosive compaction and hot-pressing under high pressure. Both methods allowed obtaining the samples of high density (up to 99% of theoretical one) and microhardness above 13 GPa. Simultaneously, a nanocrystalline structure of the material was preserved.     

Dynamic consolidation/hot isostatic pressing of SiC

Shock consolidation is a method that presents a bright potential but has been limited by inevitable cracking of compacts, especially for ceramics. In an effort to eliminate cracking while retaining the unique features of shock consolidation, three novel approaches have been implemented: (1) the use of local shock-induced reactions to increase the temperature of particle surfaces and to provide a bonding phase (reaction products); (2) shock densification at a low pressure (just above the threshold for pore collapse) followed by hot isostatic pressing; (3) shock consolidation of pre-heated specimens. These techniques were applied to silicon carbide. Reduction of cracking was observed with interparticle melting and reactions. Microstructural results, mechanical properties and advantages and limitations of these approaches are discussed. It is shown that shock consolidation of ceramics is inherently limited because shock-induced cracks are introduced into the process, damaging the particles. A criterion for the plastic deformation versus fracture of ceramic powders under shock consolidation is proposed.     

SHOCK COMPRESSION PROCESSING OF POWDERS

Shock compression processing is emerging as a novel technique for fabrication of esoteric materials. Not only can metal and ceramic powders be dynamically consolidated, but both equilibrium and non-equilibrium structures can be synthesized under the high pressure regime during the passage of shock waves of sufficient magnitude and duration. The shock waves can be generated by impact from a plate (accelerated by compressed gas or detonation of explosive) or direct contact with explosives. Very hard metallic and ceramic powders, as well as those powders that cannot be processed by conventional powder processing techniques can be easily compacted to solid densities. The bonding mechanisms in shock compaction involve the rapid and intense deposition of shock energy, preferentially at interparticle regions, resulting in extensive plastic deformation. This may lead to interparticle welding due to partial melting or simply solid-state diffusional bonding.

Shock compression processing technology will be reviewed with emphasis on the processing aspects. Specific examples of shock compaction of RSP alloys and ceramics will be presented, and feasibility of commercialization of the technique will be discussed.     

基于量纲分析的爆炸冲击波效应靶模型分析与实验研究

针对传统的冲击波压力电测法易受爆炸场寄生效应干扰问题,提出基于效应靶塑性变形的爆炸冲击波压力评定方法。由于效应靶理论模型复杂、参数较多,利用量纲分析方法简化模型获得爆炸冲击波压力作用的效应靶最大挠度与炸药TNT当量、炸高及炸距之关系,并建立冲击波压力作用的效应靶最大挠度计算模型;设计100 kg、60 kg、20 kg 三种标准TNT爆炸的立靶、平靶实验,用回归分析法获得二者经验模型系数。结果表明,立靶与平靶两种结构效应靶最大挠度实验结果与经验模型计算结果误差分别优于3.59%及3.33%。该研究可指导战斗部冲击波压力评估,进而减少爆炸实验量。     

PVDF shock sensors: applications to polar materials and high explosives

Ferroelectric polymers (PVDF) with well-defined and precisely known electrical properties are now routinely available from commercial sources. Electrical processing with the Bauer cyclic poling method can produce individual films with well-defined remanent polarization up to 9 /spl mu/C/cm/sup 2/. These polymers provide an unusual opportunity to study the structure and physical properties of materials subjected to shock loading. The behavior of PVDF has been studied over a wide range of pressures using high-pressure shock loading and has yielded well-behaved, reproducible data up to 25 GPa in inert materials. The application of PVDF gauges for recording shock waves induced in polar materials such as Kel-F, PMMA, or in reactive materials is hampered by observations of anomalous responses due to shock-induced polarization or an electrical charge released inside a shock-compressed explosive. A solution using an appropriate electrical shielding has been identified and applied to PVDF for shock measurement studies of Kel-F, and for Hugoniot measurements of high explosives (PH). Furthermore, shock pressure profiles obtained with in situ PVDF gauges in porous HE (Formex) in a detonation regime have been achieved. Typical results of shock pressure profile versus time show a fast superpressure of a few nanoseconds followed by a pressure release down to a plateau level and then by a pressure decay. More accurate measurements are reported with electrically improved PVDF gauges as well as with 0.25 mm/sup 2/ active area PVDF gauges.     

Microstructural evolutions of nickel-aluminide nanocomposites during powder synthesis and thermal spray processes

The synthesis and microstructural evolutions of the NiAl-15 wt% (Al₂O₃–13% TiO₂) nanocomposite powders were studied. These nanocomposite powders are used as feedstock materials for thermal spray applications. These powders were prepared using high and low-energy mechanical milling of the Ni, Al powders and Al₂O₃–13% TiO₂ nanoparticle mixtures. High and low-energy ball-milled nanocomposite powders were also sprayed by means of high-velocity oxy fuel (HVOF) and air plasma spraying (APS) techniques respectively. The results showed that the formation of the NiAl intermetallic phase was noticed after 8 h of high-energy ball milling with nanometric grain sizes but in a low-energy ball mill, the powder particles contained only α-Ni solid solution with no trace of the intermetallic phase after 25 h of milling. The crystallite sizes in HVOF coating were in the nanometric range and the coating and feedstock powders showed the same phases. However, under the APS conditions, the coating was composed of the NiAl intermetallic phase in the α-Ni solid solution matrix. In both of the nanocomposite coatings, reinforcing nanoparticles (Al₂O₃–13% TiO₂) were located at the grain boundaries of the coatings and pinned the boundaries, therefore, the grain growth was prohibited during the thermal spraying processes.     

Explosion synthesis of Ti5Si3-Cu intermetallic compound

Synthesis of an intermetallic compound based on Ti₅Si₃ by an explosive compaction of elemental powders was studied with the detonation velocity as the main experimental variable. Prior to the explosion experiment, a computer simulation of the compaction process was conducted by using the DYNA program, and the result was utilized in designing the experiment. The relative density of the compacted compound increased with the detonation velocity. To enhance the density of the compound further, however, it was necessary to adjust other variables associated with the can, powder, and the backup tube. From an X-ray diffraction analysis of the explosion-compacted compound, it was confirmed that formation of the Ti₅Si₃ phase was complete. Although there is a room for further improvement of the density and the crack resistance of the compacted alloy, the present work verified that explosion synthesis is a potentially viable method to consolidate intermetallic compounds.     

Reaction-sintered hot-pressed TiAl

Titanium aluminide intermetallic alloys and composites were formed from elemental titanium and aluminium powders by self propagating, high-temperature synthesis in an induction-heated hot-press. The crystal phases, density, transverse rupture stress, and hardness of the reaction-sintered compacts, were observed to be controlled by hot-pressing conditions. The principal phase formed was TiAl together with a significant second-phase concentration of Ti₃AI. The transverse rupture strength (TRS) of the intermetallic composites was observed to vary directly with compact density. Under selected high-temperature synthesis hot-pressing conditions, TRS values were comparable to those obtained for fully dense TiAl. Titanium aluminide composites were formed by adding boron, carbon, silicon and Al₂O₃, and SiC powders and whiskers to the Ti-Al powders before reaction sintering. Changing the alloying additions did not have as strong an effect on properties of the composite compacts as did varying hot-pressing conditions.     

Liquid-Phase Shock-Assisted Consolidation of Superconducting MgB<Subscript>2</Subscript> Composites

An original two-stage liquid-phase hot explosive compaction (HEC) procedure of Mg-B precursors above 900 ^°C provides the formation of superconductivity MgB₂ phase in the whole volume of billets with maximal T _c = 38.5 K without any further sintering. The liquid-phase HEC strongly increases the solid-state reaction rate similar to photostimulation, but in this case, due to the high penetrating capability of shock waves in a whole volume of cylindrical billets and consolidation of MgB₂ precursors near to theoretical density allows one to produce bulk, long-body cylindrical samples important for a number practical applications.     

双层爆炸复合中覆板最小可焊厚度的分析

为了研究双层爆炸焊接中覆板的最小可焊厚度,分析了爆炸焊接对于炸药布药量的要求,提出了一种利用爆炸焊接的碰撞速度下限与覆板的一维平板运动公式计算爆炸焊接中覆板最小可焊厚度的方法,并采用爆炸焊接中常用的3种炸药,分别对不锈钢-钢、铝-钢、钛-钢、铜-钢的爆炸焊接最小可焊厚度进行计算,计算得出4种覆板的最小可焊厚度分别在1.5、2.5、2.0、1.5 mm左右。同时指出在进行小厚度覆板的爆炸焊接时,由于密度更低的炸药爆轰压力也更低,可以更好地适用于小厚度覆板的爆炸焊接。     

钛-钢板爆炸焊接的影响因素及炸药配方

爆炸复合用炸药是影响爆炸焊接效果的最主要因素,不同的材料和工艺参数对炸药的爆速、比冲量和能量有不同的影响,其中炸药的密度直接影响复板斜碰撞基板的速度和角度。选用低合金高强度结构钢Q345B和工业纯钛TA2为实验材料,通过理论计算与实验研究,得到了一种较为适合钛-钢板爆炸焊接用的炸药配方,并对钛-钢爆炸焊接影响因素进行了探讨。     

SUS304不锈钢/Q345R碳钢爆炸焊接工艺参数研究

针对实际生产中在爆炸焊接窗口内取值时因为所取参数不同而导致生产的复合板结合强度差异较大这一现状,通过对SUS304不锈钢／Q345R碳钢爆炸焊接窗口内不同工艺条件得到的复合板进行剪切强度测试及金相分析,得到界面结合强度与界面波形的关系以及两者随工艺参数的变化规律,找到窗口内最佳的工艺参数,以提高爆炸焊接复合板质量以及生产效益。研究表明：界面波形的波长和振幅随着装药量的增加而增大,随基复板间距的增加先增大后减小。爆炸焊接窗口内最佳工艺参数取值范围与复板厚度有关。复板为薄板（3mm）时,取得最佳结合强度时界面波形波长为1250μm左右,振幅为200μm左右,对应的最佳装药质量比为1．02,基复板间距为8mm,取值比理论最佳值偏高;复板为厚板（6mm）时,取得最佳结合强度时界面波形波长为900岫,左右,振幅为100μm左右,对应的最佳装药质量比为0．45,基复板间距为14mm,取值靠近下限。当界面波长与振幅相同时,复板为薄板的结合强度要高于厚板。