Explosive Hardening Research Articles

Novel methods for the control of blast noise from explosive depth hardening

DNV Spadeadam undertakes crucial major hazards testing to improve safety across a wide range of industries, including energy and infrastructure. One common form of testing is Explosive Depth Hardening (EDH) in which plastic explosives up to 10 kg TNT are used to harden pre-cast railway crossings in order to support national transport infrastructure. The operations produce extremely high intensity noise and are carried out up to 10 times per day. The source characteristics of the explosion are not well understood and vary significantly with operational demands. This has implications on occupational and environmental blast noise impacts. Quantification of the source characteristics are important for the exposures of site personnel with regards to providing adequate hearing protection. Moreover, for the purpose of managing environmental noise impacts on local communities, the uncertainties around source directivity and strength make long-range blast noise prediction difficult. This paper presents the current research on novel blast noise mitigation undertaken in the laboratory, such as experimental water curtains, water sprays, and metamaterial designs. It is proposed to implement novel methods developed in the laboratory for use during EDH shots at full-scale, and the potential improvements to occupational and environmental noise impacts will be discussed.

A Comprehensive Study of a Novel Explosively Hardened Pure Titanium Alloy for Medical Applications.

Pure titanium is gaining increasing interest due to its potential use in dental and orthopedic applications. Due to its relatively weak mechanical parameters, a limited number of components manufactured from pure titanium are available on the market. In order to improve the mechanical parameters of pure titanium, manufacturers use alloys containing cytotoxic vanadium and aluminum. This paper presents unique explosive hardening technology that can be used to strengthen pure titanium parameters. The analysis confirms that explosive induced α-ω martensitic transformation and crystallographic anisotropy occurred due to the explosive pressure. The mechanical properties related to residual stresses are very nonuniform. The corrosion properties of the explosive hardened pure titanium test do not change significantly compared to nonhardened titanium. The biocompatibility of all the analyzed samples was confirmed in several tests. The morphology of bone cells does not depend on the titanium surface phase composition and crystallographic orientation.

Fabrication of large-depth and multiscale gradient microstructure in dual-phase high entropy alloy via shock loading

Large-depth and multiscale gradient microstructure in dual-phase Al0.6CoCrFeNi high entropy alloy (HEA) were fabricated by explosion hardening (EH) technique. The gradient microstructure evolution was investigated in detail. The microhardness distribution and tensile properties near EH affected surface were also determined. The formation and strengthening mechanisms of gradient microstructure after EH treatment were subsequently analyzed. Experimental results showed that the multiscale gradient microstructure in terms of grain size, phase morphology, dislocation structure, texture was induced in dual-phase (BCC + FCC) HEA by EH technique. The closer to EH affected surface, the finer grain size, higher dislocation density and stronger texture intensity. The deformation and break of spinodal decomposition and formation of new grain boundaries by dislocation structure contributed to grain refinement and transition of equiaxed grains to dendritic grains from lower area to EH affected surface. After EH treatment, the microhardness generally increased with a maximum increase of ∼67% within 5 mm from EH affected surface, the tensile yield stress increased from 320 MPa to maximum of 700 MPa. The strengthening mechanism is different at various depth positions: near EH affected surface, the main strengthening mechanism is high-density dislocations, stacking faults and grain refinement; in areas relatively far from EH affected surface, only dislocation structure contributed to the strengthening of mechanical properties.

Dynamic shear properties and microstructure evolution of commercially pure titanium with heterogeneous gradient microstructure

Heterogeneous gradient microstructure in commercially pure titanium (CP Ti) was fabricated through the explosion hardening (EH) technique followed by annealing treatment (AT). The heterogeneous gradient microstructure was characterized by a microhardness tester, optical microscope and transmission electron microscope. Subsequently, dynamic shear properties and microstructure evolution of the material were systematically studied by split Hopkinson pressure bar apparatus with hat-shaped shear specimens. Experimental results showed that various heterogeneous gradient microstructures were obtained by EH + AT at different annealing temperatures. Enhanced dynamic shear properties with special yield stress-fracture strain combinations were observed, exhibiting better mechanical properties than the other metallic materials. Such excellent mechanical properties originated from finer grain size, higher twin/dislocation density and gradient synergistic effect. During dynamic shear tests of gradient CP Ti, adiabatic shear bands (ASBs) were easy to nucleate, propagate and interact, especially on EH treated specimen surface due to the generation of high-density micro-defects. Formation of twins/dislocations during EH treatment promoted dynamic recovery during the ASBs nucleation stage, whereas AT delayed ASBs nucleation due to a decrease in micro-defects, which contributed to better ductility. During dynamic shear tests of gradient CP Ti, propagation of ASBs and cracks was delayed by the gradient microstructure. The adiabatic temperature rise of 2-EH treated CP Ti was calculated to be 108 °C when ASBs nucleated, which was so low that it was supposed to have no effect on ASBs nucleation.

Research on the post-weld explosive hardening of AA7075-T651 friction stir welded butt joints

Research on the post-weld explosive hardening of AA7075-T651 friction stir welded butt joints

Research on Explosive Hardening of Titanium Grade 2.

In this investigation, three different explosive materials have been used to improve the properties of titanium grade 2: ammonal, emulsion explosives, and plastic-bonded explosives. In order to establish the influence of explosive hardening on the properties of the treated alloys, tests were conducted, including microhardness testing, microstructure analysis, and tensile and corrosion tests. It has been found that it is possible to achieve a 40% increase in tensile strength using a plastic explosive (PBX) as an explosive material. On the other hand, the impact of the shock wave slightly decreased the corrosion resistance of titanium grade 2. The change in corrosion rate is less than 0.1µm/year, which does not significantly affect the overall corrosion resistance of the material. The reduction in corrosion resistance is probably due to the surface geometry changes as a result of explosive treatment.

Enhancement of mechanical properties of commercially pure titanium by shock induced gradient microstructure with martensitic transformation

In the present work, explosion hardening (EH) technique was used to produce gradient microstructure with martensitic transformation in commercially pure titanium (CP Ti) to improve its mechanical properties. After EH treatment, phase structure, grain size distribution, dislocation structure and twin structure in CP Ti were characterized. Subsequently, microhardness tests, tensile/compressive tests and three-point bending tests were conducted to investigate mechanical properties of EH treated CP Ti along different depth positions from EH treated surface. Experimental results show that gradient microstructure in terms of grain size, α-ω martensitic transformation, texture intensity, twin density, dislocation density and hierarchical nanotwins, are observed in EH treated CP Ti. According to microstructure characteristics, four layers including nanostructure surface layer, refined structure layer, deformed coarse grained layer and coarse grained matrix are divided from EH treated surface to matrix. Microhardness tests show a gradient hardness layer with a maximum hardness increase of 83% within 3.5 mm from EH treated surface. Tensile and compressive test results show that the most significant strengthening exists within 2 mm depth from EH treated surface with a maximum tensile yield stress increase of 71% and the total EH affected depth is more than 25 mm. In addition, the gradient microstructure is affected by the number of EH treatments. For example, bending yield stress increases by 41.3% in 1-EH treated specimens and 64.8% in 2-EH treated specimens. Combining microstructure characterization and mechanical properties testing, shock-induced strengthening mechanism of CP Ti is analyzed: for positions close to EH treated surface, formation of α-ω martensitic transformation and grain refinement is responsible for the significant strengthening phenomenon; whereas, for positions far away from EH treated surface, the moderate strengthening phenomenon is due to the generation of high-density dislocations/twins.

Shock induced gradient microstructure with hierarchical nanotwins to enhance mechanical properties of Ti6Al4V alloy

In the present work, Ti6Al4V alloy was treated by one/two passes explosion hardening (EH) technique to enhance mechanical properties. The phase structures, grain size distribution, dislocation and twin structures of EH treated Ti6Al4V alloy were characterized in detail. Mechanical properties of EH treated Ti6Al4V alloy were measured by tensile and compressive tests. The mechanism of shock-induced strengthening was subsequently analyzed. Experimental results showed that gradient grain microstructure with nanotwins/hierarchical nanotwins and β-α phase transformation occurred near the surface of EH treated Ti6Al4V alloy. Furthermore, the tensile and compressive strengths of Ti6Al4V alloy exhibited significant enhancement after EH treatment. The compressive strength of the materials increased from 1008 MPa in untreated condition to 1121 MPa in one pass EH treatment and 1365 MPa in two passes EH treatment, while the fracture strains always remained more than 0.15. The significant strengthening of Ti6Al4V alloy after two passes EH treatment was mainly attributed to the formation of hierarchical nanotwins, which can effectively impede dislocation motion. In summary, EH is an effective technique to improve mechanical properties of Ti6Al4V alloy by producing gradient microstructure with hierarchical nanotwins. The present research may have the potential use for metallic materials in the field of load-carrying capacity, tribological property and fatigue property. • Gradient microstructure with hierarchical nanotwins was produced by explosion hardening. • After two passes explosion hardening, compressive strength of Ti6Al4V increased by 35.4%. • Both twin-dislocation wall interactions and twin-twin interactions contributed to grain refinement. • Shock strengthening was mainly due to the formation of hierarchical nanotwins, which effectively impedes dislocation motion.

The concept of improvement high-strength aluminum alloys FSW joint properties via post-weld explosive treatment

The study describes the theoretical background and technological aspects of the post-weld explosive treatment of high-strength aluminum alloy FSW joints. Although FSW allows to effective join high-strength aluminum alloys, the heat generated during the process causes undesirable changes in the strengthening phase, giving a joint efficiency of about 80%. The load-carrying capabilities of these joints can be increased via post-weld treatment (e.g. shot peening, laser shock peening). The new, potential post-weld treatment that is presented in this paper is based on the affection of the welded joint by a shock wave generated during the detonation of explosive material. Such post-weld explosive treatment would result in the hardening of the low-hardness zone, which often determines the mechanical properties of precipitation-hardened aluminum alloy FSW joints. Studies show that explosive welding of annealed aluminum alloys increases their microhardness by about 25% as the result of a high-velocity collision. If a similar effect can be achieved in explosive hardening, the microhardness of the low-hardness zone will increase entailing an improvement of entire joint mechanical properties. The variety of explosives materials used in metalworking (covering the values of detonation velocity from about 2000 m/s to 8000 m/s) and different systems for shock-wave affection gives many technological possibilities. In this work are discussed two different explosive hardening systems: with direct placement of explosive material on a treated welded plate and with an additional driven plate, which provides a higher pressure impulse. Considering that affecting of high amplitude shock wave introduces defects into the structure and decreases residual stresses in the welded joints, the application of an appropriate technological system creates a potential for improving the load-carrying capacities of discussed joints, especially in a condition of cyclic loading.

ЗАСТОСУВАННЯ ТЕХНОЛОГІЇ ІМПУЛЬСНОЇ ОБРОБКИ МЕТАЛІВ ДЛЯ БРОНЕЗАХИСТУ СПЕЦІАЛІЗОВАНОГО ТРАНСПОРТУ

Purpose. Increasing the technical and economic indicators of the technology of impulse processing of metals and means of their diagnostics based on the development of the theoretical foundations of shape change under the impulse impact and the calculation of power parameters. Methodology. Numerical simulation of explosive loading of a plate made of Quardian 500 steel was performed in the Ansys AUTODYN system using a description of the properties of the material subjected to impulse impact and an iterative procedure. The calculation system included atmospheric air, an explosive charge (9.9 kg of trinitrotoluene), a striker plate, a test plate and soil. Results. An experimental study of the dynamic explosive load of Quardian 500 steel has been carried out and the results have been compared with the analytical calculations obtained in the Ansys AUTODYN system using the developed iterative procedure. Adequacy of the developed mathematical model of the numerical study of the explosive load to the results of the natural experiment has been determined. Scientific novelty. The solution of this problem can be used in the future to evaluate the plastic properties of materials during welding and explosion hardening, as well as during explosion stamping of blanks and the combination of welding and explosion stamping operations; with impulse stamping methods - magnetic-pulse, electro-hydraulic, gas detonation, etc., when part of the workpiece collides with the matrix, and the other part continues to deform; when stamping on hammers; when crushing materials by the impact of a rigid body; explosion fragmentation of multicomponent environments and determination of ballistic resistance of elements of combat and special equipment. Scientific significance. The developed mathematical model can be used to evaluate the protection of machine crews and increase the level of tactical and technical characteristics during demining.

Shock-induced large-depth gradient microstructure in commercial pure titanium subjected to explosive hardening

Explosive hardening of commercial pure titanium plate was conducted by a thin-layer high-detonation-velocity explosive. The nanoindentation and Vickers hardness tests of the treated titanium plates along the depth of shock loading were performed. The microstructures along the depth were characterized by using different methods, including X-Ray Diffraction, Optical Microscopy, Electron Back-Scattered Diffraction and Transmission Electron Microscopy. Experimental results showed that large-depth gradient hardness distribution with depth of 2.5 mm was produced in CP titanium by explosive hardening. There are two gradient hardenedlayers, ultra-hardened layer with a depth of 0–40 μm and a hardness increase of ∼400%, sub-hardened layer with a depth of 40 μm-2500 μm and a hardness increase of 54.3%. Gradient microstructures with different characteristics were observed, including gradient α-ω phase transition, gradient grain size, gradient twining and gradient dislocation. The area of gradient microstructure is consistence with that of gradient hardness distribution. Grain refinement/α-ω phase transition mainly contributed to hardness sharply increasing in ultra-hardened layer. High-density dislocation/twining mainly contributed to hardness increasing in the sub-hardened layer. Finally, the formation mechanism of gradient microstructures and grain refinement mechanism was detailly discussed.

Dynamic behavior and adiabatic shearing formation of the commercially pure titanium with explosion-induced gradient microstructure

The commercially pure (CP) titanium has been processed by explosion hardening to produce a gradient microstructure. The hardness distribution of CP titanium after explosion hardening was measured. The microstructure of explosion hardened CP titanium was revealed by transmission electron microscopy and optical microscopy. The split Hopkinson pressure bar was used to study the effect of explosion hardening on dynamic behavior and adiabatic shearing formation of CP titanium. The experimental results showed that explosion hardening induced the gradient hardened microstructure with a depth of 2.6 mm in CP titanium. The explosion hardened specimens present enhanced static and dynamic compressive strengths, which was caused by grain refinement, the α-ω phase transition, and micro-defects’ proliferation. The gradient deformation and gradient ASB occurred in explosion hardened specimen after dynamic loading, whereas the homogeneous deformation and a bipyramid-shaped adiabatic shear band were observed in untreated specimen. The ASBs were easier to nucleate, propagate, bifurcate and interact in the explosion hardened CP titanium during dynamic loading, especially in the shocked side due to the higher-density micro-defects. This was attributed that the ω phase particles and the proliferation of twinning/dislocations during explosion hardening promoted the dynamic recovery process during the nucleation stage of ASBs. The gradient microstructure in CP titanium with explosion hardening delayed the propagation of ASBs and cracks under dynamic loading.

Optimization of the combined explosion hardening processes

The proposed method for calculating the loading parameters makes it possible to determine the wear parameters after explosion hardening. The calculation method is simple and less time consuming compared with calculation methods that involve the use of nonlinear programming methods. The main methods of increasing the wear resistance of mining equipment parts using explosion methods are generalized. The reserve for increasing the wear resistance consists in the optimization of deformation parameters during the power and thermal intensification of processes and the development of new methods and technologies of hardening. The factors (parameters) of the studied processes: explosive cladding, alloying, hardening, are formulated. Optimization of the processes under consideration is possible by decomposing the process into simpler ones with subsequent optimization of the parameters of these processes and the synthesis of the obtained solutions. For the first time, a solution to the multicriteria problem of two-stage explosion hardening is presented. It is proposed to split the process into simpler ones. Optimization criteria are proposed for each of the simplified processes. The problem is reduced to a conditional extremum problem, which is solved by composing the Lagrange function. By transforming the wear equation, the optimal ratio of strength and ductility for parts operating under abrasive wear conditions is determined.

Studying the Impact of Blast Treatment on the Structure and Mechanical Properties of Carbon Steel

The study has covered the effects of blast treatment on the microstructure parameters and mechanical performance of carbon steel. The calculation results of examining the structure and properties of carbon steel in its initial state and after explosive hardening in various sections of cylindrical carbon steel workpieces have been verified with the finite-element analysis using the ANSYS Workbench software environment. Blast treatment has been demonstrated to lead to a perceptible change in the structural state of carbon (cementite) in steel.

Obróbka wybuchowa i cieplno-chemiczna wielowarstwowych kompozytów metalicznych

The paper describes methods for the explosive hardening of metals which were performed with a view to increasing the hardness of previously obtained composites, as well as treatment of their surface layers to increase the efficiency of further thermochemical treatment. Typical systems for explosive hardening of metals and the construction of current systems, are discussed. The resulting effects of explosive hardening are illustrated with before and after diagrams of microhardness distributions in cross-sections of the processed composites hardening. In a further processing stage, the tested composite samples were subjected to ion nitriding. As a result of this process, in addition to the typical increase in hardness of the individual layers, an intermediate phase with a distinctly higher hardness was observed in the junction zone. Preliminary analysis of the photographs and the results from a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment suggests that the particularly beneficial properties of the composites are attributed to the presence of the intermetallic layer.

Enhancement of Mechanical Properties of AISI304 Stainless Thin Plate by Low-pressure, Repeated Explosive Hardening

Enhancement of Mechanical Properties of AISI304 Stainless Thin Plate by Low-pressure, Repeated Explosive Hardening

AN ANALYSYS OF WEAR AND MECHANICAL AND TRIBOLOGICAL PROPERTIES OF HIGH-MANGANESE CAST STEEL HARDENED BY DIFFERENT METHODS

Properties of high manganese austenitic cast steel are not satisfactory; therefore, this material should be hardened. Currently, the commonly used method of hardening does not allow eliminating problems related to premature wear of railway frogs. Therefore, many studies have been carried out to find an alternative method to obtain improved wear resistance of such elements. The article presents an analysis of the mechanical and tribological properties of base and hardened, by different methods, high-manganese cast steel applied for turnouts. Tests were performed for three hardening methods: explosive, pressure-rolling, and dynamic impact. The results were compared with the properties of base material after saturation treatment. The conducted tests allowed the determination of hardness profiles of hardened surfaces, as well as the wear resistance and coefficient of friction, and the obtained results are very promising. Hardening by dynamic impact provided much better results in relation to presently used explosive hardening technology.

Упрочнение взрывом и его применение в производстве крестовин железнодорожных стрелочных переводов

Упрочнение взрывом и его применение в производстве крестовин железнодорожных стрелочных переводов

Metal explosion chambers: designing, manufacturing, application

Designing of explosion chambers is based on research investigations of the chamber body stress-strain state, which is determined by numerical computation and experimentally by the strain gage technique. Studies show that chamber bottoms are the most loaded elements, and maximal stresses arise in chamber poles. Increasing the shell thickness around poles by welding-in an insert is a simple and saving way to solve this problem. There are structural solutions, enabling reliable hermetic closure and preventing leakage of detonation products from the chamber. Explosion chambers are employed in scientific research and in different industrial applications: explosive welding and hardening, synthesis of new materials, disposal of expired ammunition, and etc.

High Energy Rate Forming Induced Phase Transition in Austenitic Steel

In this study, the effects of explosion hardening on the microstructure and the hardness of austenitic stainless steel have been studied. The optimum explosion hardening technology of austenitic stainless steel was researched. In case of the explosive hardening used new idea means indirect hardening setup. Austenitic stainless steels have high plasticity and can be cold formed easily. However, during cold processing the hardening phenomena always occurs. Upon the explosion impact, the deformation mechanism indicates a plastic deformation and this deformation induces a phase transformation (martensite). The explosion hardening enhances the mechanical properties of the material, includes the wear resistance and hardness [1]. In case of indirect hardening as function of the setup parameters specifically the flayer plate position the hardening increased differently. It was find a relationship between the explosion hardening setup and the hardening level.