SHS Compaction Research Articles

Effect of Mechanical Activation and Combustion Parameters on SHS Compaction of Titanium Carbide

Effect of Mechanical Activation and Combustion Parameters on SHS Compaction of Titanium Carbide

SHS Compaction of TiC-Based Cermets Using Mechanically Activated Mixtures

SHS Compaction of TiC-Based Cermets Using Mechanically Activated Mixtures

Forced SHS Compaction of TiC–NiTi Composites

Forced SHS Compaction of TiC–NiTi Composites

Forced SHS Compaction of TiB2–Ti: Structure and Properties

Forced SHS Compaction of TiB2–Ti: Structure and Properties

Convective Combustion of a Mechanically Activated Ti + C Mixture under Forced SHS Compaction

Convective Combustion of a Mechanically Activated Ti + C Mixture under Forced SHS Compaction

Forced SHS Compaction of NiTi

Forced SHS Compaction of NiTi

SHS compaction of TiC cermets using mechanically activated mixtures

This paper focuses on obtaining cermet composite materials by SHS compaction. The study covers the effect of mechanical activation of metal components contained in reaction mixtures based on the Ti + C + Cr + Ni system when treated with grinding media in a ball mill. Two mechanical activation methods were used for Ti, Cr and Ni metal powders. In the first method, Cr and Ni powders were activated with grinding media separately from other reaction mixture components, and then mixed with titanium and carbon black powders. It is shown that the preliminary mechanical activation of inert components reduces the temperature and rate of combustion and increases the average size of carbide grains. In the second method, Ti + + Cr, Ti + Ni, and Ti + Cr + Ni powder mixtures were jointly processed in a ball mill, and then mixed with carbon black. This method provided mechanical activation of titanium particles with a minimum effect of grinding media on Cr and Ni powders. This led to an increase in the combustion rate and temperature, a decrease in the average size of carbide grains, and an increase in the composite structure homogeneity. A mechanism is proposed for the interaction of reagents (Ti + C) with the participation of activated Cr and Ni particles in combustion and structure formation zones, according to which the mechanical activation of inert components leads to their direct participation in the reaction interaction of titanium with carbon, which determines a decrease in the combustion rate and temperature and affects the fineness and structural homogeneity of compact composites. The results obtained were used to increase the structural homogeneity and fineness of the STIM-3B composite (Grade 3B synthetic hard tool material).

Effect of mechanical activation and combustion parameters on titanium carbide SHS compaction

The paper presents the results of a study on the dense titanium carbide production by SHS compaction. It is shown that the use of a mechanically activated reaction mixture of titanium and carbon black powders makes it possible to obtain titanium carbide samples with a maximum relative density of 95 %. A feature of this research is that the mechanical activation of components and Ti + C mixture stirring were carried out in a ball mill. The study covers the influence of process parameters on the combustion properties and structure of the consolidated titanium carbide. It was found that the high-speed reaction mixture combustion is an essential condition for dense titanium carbide production. It was shown that the burning rate and temperature strongly depend on the size, mass and density of charge compacts. With an increase in the diameter (20–58 mm) and weight (10–70 g) of compacts made of mixtures with activated reagents, the burning rate varied from 10 to 100 cm/s, and the burning temperature varied from 2200 to 3100 °C. An influence of the pre-pressing pressure (applied at the combustion stage) on the burning rate and temperature was shown: the burning rate sharply decreases from 100 to 10 cm/s at pressures between 0 and 10 MPa, and the combustion temperature decreases monotonically from 3000 to 2000 °C at pressures between 0 and 40 MPa. A high-speed combustion mechanism was proposed for the titanium and carbon black reaction mixture where the formation of radial (longitudinal) cracks in compacts pressed from the mechanically activated mixture is an important factor. These cracks ensure the propagation of incandescent impurity gases and the exothermic reaction initiation in the sample volume.

TiC–20% Cr(Ni) Composites by Forced SHS Compaction: Influence of Mechanical Activation Mode

TiC–20% Cr(Ni) Composites by Forced SHS Compaction: Influence of Mechanical Activation Mode

Mo5SiB2-Based Ceramics by Forced SHS Compaction and Hot Pressing of SHS-Produced Powders: Features of Phase-Formation Processes

Mo5SiB2-based ceramics were fabricated from elemental powders by forced SHS compaction and hot pressing of SHS-produced powders and specific features of product patterning were characterized by XRD, time-resolved XRD, SEM/EDS, and TEM/EDS. Best results were obtained upon hot pressing of SHS-produced Mo–Si–B powders: resultant material was single-phased Mo5SiB2 with a mean grain size of 2–10 μm.

Hard Alloy Production by SHS Compaction in Open Matrix

The possibility of performing SHS for the composition (wt %) 81.5Ti + 18.5B in air with subsequent compaction of combustion products in an open steel mold with the walls limiting their radial flow under severe heat dissipation conditions without using an intermediate loose heat insulator is investigated. The preparation modes of reaction powder mixtures to the synthesis is optimized. Process characteristics such as loose density, densification, and elastic aftereffect are performed, and the strength of compacts is evaluated. It is shown that the interrelation between the strength of charge compacts, combustion rate, and variation in the volume after combustion in air occurs. The optimal density of charge compacts is found to be 0.75, which corresponds to the maximum combustion rate without charge escapes and with a minimum change in volume. As a result of the optimization, the possibility of an efficient and safe synthesis process without using an intermediate insulator friable medium is shown. Hard-alloy plates 60 mm in diameter and 11 mm in thickness are prepared under the conditions of SHS compaction in an open steel mold. The structure of prepared hard alloy is unique with porosity smaller than 0.5% and consists of titanium diboride (~60 wt %) and binder titanium-based phase (~40 wt %). Such a structure, formed due to accelerated cooling, can be determined as nonequilibrium according to the phase diagram of the Ti–B system; titanium monoboride (TiB) should be the main phase for the composition under investigation. The microhardness of the fabricated hard alloy is HV = 18 000 MPa.

Forced SHS Compaction of Ti–B Blends: Influence of Mixing Conditions and Sample Mass

We explored the influence of mixing (milling) conditions and sample mass on forced SHS compaction of equiatomic Ti–B blends. An increase in mill/ball ratio was found not only give start to mechanochemical synthesis but also affected the processes of combustion and product patterning. The mass of green compacts did not affect combustion temperature. Our results may turn interesting to those engaged in combustion synthesis of new materials.

Hard alloy production by SHS compaction in an open die

The paper investigates the possibility of carrying out SHS for the Ti (81.5 wt.%) + B (18.5 wt.%) composition in the air followed by pressing combustion products in an open steel die with walls limiting their radial flow under tough heat dissipation conditions without the use of an intermediate loose medium of the heat insulator. Modes of reaction powder mixture preparation for synthesis were optimized. Such process characteristics as bulk density, compaction, elastic aftereffect were determined for initial powders and reaction mixtures, and the strength of compactions was estimated. It is shown that there is a relationship between the strength of charge compacts, combustion rate and changes in their volume after combustion in the air under intensive gas liberation during combustion. The optimal charge compact density was found equal to 0.75 corresponding to the maximum combustion rate without charge emissions with a minimum change in volume. As a result of the optimization, the possibility of effective and safe conduct synthesis process without the use of an intermediate loose medium of the heat insulator is shown. Hard-alloy plates with a diameter of 60 mm and a thickness of 11 mm were obtained in the open steel die under SHS compaction conditions. The structure of the resulting hard alloy is unique with a porosity of less than 0.5 %. It consists of titanium diboride (~60 wt.%) and titanium-based binder phase (~ 40 wt.%). Such a structure obtained as a result of accelerated cooling can be defined as nonequilibrium, since the main phase for the studied composition should be titanium monoboride (TiB) in accordance with the Ti–B state diagram. The microhardness of the fabricated hard alloy is HV = 18000 MPa.

External Friction in SHS Compaction

Reverse pressing under the active action of external friction force was theoretically analyzed based on the previously developed rheodynamic models of high-temperature SHS compaction. It was shown that, in this pressing method, external friction is a useful technological phenomenon, which allows one to reach a uniform density distribution in the bulk of the material of the workpiece. Analytical expressions for calculating the characteristic pressing time and the pressure distribution were obtained.

Structure Formation in Ti/Ti–Al–C Layered Ceramic Materials Obtained by the Method of Unconfined SHS Compaction

We present the results of the experimental investigations of the phase and structure formation in a layered ceramic material based on the MAX phase in the Ti/Ti–Al–C system obtained under the conditions of combination of combustion processes with high-temperature shear deformation (SHS compaction). We analyze the specific structural features of the developed material and the character of interaction between the products of synthesis and the surface layer of titanium substrate.

Synthesis and Properties of Composites Based on Zirconium and Chromium Borides

Experimental data on the fabrication of composites based on the ZrB2–CrB system by SHS compaction are presented. Adiabatic combustion temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products are calculated using the thermodynamic data, and optimal fabrication conditions for SHS composite production are determined. It is shown that the equilibrium synthesis products are ZrB2 and CrB refractory compounds. They provide the high thermodynamic stability of SHS composites, which are applied as a dispersed phase (ZrB2) and ceramic binder (CrB). The adiabatic combustion temperature decreases from 3320 to 2350 K with an increase in the binder content from 25 to 64 wt %. A hard dispersed phase (ZrB2) and molten binder (CrB) are formed under these conditions. It is revealed that the formation of a molten binder provides the formation of SHS composites with residual porosity lower than 1%. The influence of the composition of the reaction mixture on the phase composition, microstructure, and physicomechanical characteristics of SHS composites are investigated. It is established that the residual porosity at the CrB content in the limits of 30–50 wt % is <1%. Herewith, the Vickers hardness varies in a range of 31.3–42.6 GPa, while the ultimate bending strength varies in a range of 480–610 MPa. It is shown that physicomechanical characteristics depend on the residual porosity of SHS composites. Cutting plates are fabricated from the ZrB2–30CrB SHS composite and testing is performed with the treatment of high-hardness chilled steels. The results evidence that ceramic cutters made of the ZrB2–30CrB composite possess high wear resistance when treating ShKh15 bearing steel with hardness of 61–65 HRC.

Production of Large Compact Plates from Ceramic Powder Materials by Free SHS Compaction

Free SHS compaction was tested as a method for producing large compact plates more than 100 mm in size from powders of high-melting inorganic compounds based on titanium diboride. Materials science studies of the obtained plates were performed, and their physicochemical properties were investigated. The synthesized material was heat-resistant at temperatures to 1100°C.

SYNTHESIS AND PROPERTIES OF COMPOSITES BASED ON ZIRCONIUM AND CHROMIUM BORIDES

This paper provides experimental data on ZrB2–CrB composite production by SHS compaction. Thermodynamic data were used to calculate adiabatic flame temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products and to determine optimum conditions for SHS composite production. It was shown that equilibrium products of combustion synthesis are ZrB2 and CrB refractory compounds that ensure high thermodynamic stability of SHS composites. They are used as a dispersed phase (ZrB2) and a ceramic binder (CrB). As the binder content increases from 25 to 64 wt.%, the adiabatic combustion temperature decreases from 3320 to 2350 K. A solid dispersed phase (ZrB2) and a molten binder (CrB) are formed at these conditions. It was identified that SHS composites with a residual porosity less than 1% can be produced due to molten binder formation. The effect of reaction mixture composition on the phase composition, microstructure, physical and mechanical properties of SHS composites was studied. It was found that the residual porosity of SHS composites is ~1 % at the 30–50 wt.% CrB content. Vickers hardness is 31,3 to 42,6 GPa, and flexural strength is 480 to 610 MPa. It was shown that physical and mechanical properties depend on the residual porosity of SHS composites. The obtained ZrB2– 30CrB SHS composite was used to make cutting inserts and conduct tests for high-strength hardened steel machining. The test results proved that ZrB2–30CrB ceramic inserts feature high wear resistance when machining ShKh15 chromium bearing steel with a hardness of 61–65 HRC.

FEATURES OF PRODUCTION AND HIGH-TEMPERATURE OXIDATION OF SHS-CERAMICS BASED ON ZIRCONIUM BORIDE AND ZIRCONIUM SILICIDE

The paper is dedicated to the study of kinetics and combustion mechanism of reaction mixtures in Zr–Si–B and Zr–B systems, production of compact ceramic materials in a process of SHS compaction, as well as studying their heat resistance. The paper demonstrates that temperature and combustion speed dependencies of compounds in the Zr–Si–B system on the initial temperature (T 0 ) are linear, i.e. with a rise in T 0 , staging of chemical reactions of zirconium diboride and disilicide formation does not change. The paper calculates values of the effective SHS process activation energy, which demonstrate the crucial role of the reaction interaction between zirconium and boron and silicon in a melt. The paper studies the staging of chemical reactions in a mixture Zr–Si–B combustion wave: initially, the ZrB 2 phase is formed from the melt by crystallization, then the ZrSi 2 phase appears with a delay of 0,5 s and 1 second later unreacted Si crystallizes. The paper studies the phase composition of synthesis products with diboride ZrB 2 as a main component and zirconium disilicide ZrSi 2 , Si and boride ZrB 12 depending on the initial reaction charge composition. The new compact samples characterized by high hardness and low residual porosity were produced in the process of power SHS compaction. Formation of oxide films SiO 2 –ZrO 2 –B 2 O 3 along with the complex oxide ZrSiO 4 , which serve as an effective diffusion barrier and reduce the oxidation rate, occurs on the surface of SHS-samples in response to their high-temperature oxidation and depending on their composition.

Production of ultra-high temperature carbide (Ta,Zr)C by self-propagating high-temperature synthesis of mechanically activated mixtures

The combustion temperatures and rates of mechanically activated (MA) Ta–Zr–C mixtures depending on the initial temperature T0 are determined. The self-heating phenomenon is observed in argon atmosphere at T0>380K due to oxidation of the surface of zirconium particles by adsorbed oxygen. Zirconium oxide is formed in the combustion zone at the initial stage of chemical interaction; it is subsequently transformed into zirconium carbide. In addition, tantalum carbide is formed in the combustion zone, while the binary tantalum–zirconium carbide (Ta,Zr)C is formed closer to the post-combustion zone. In order to maintain the layer by layer stationary combustion mode of SHS, the initial temperature T0 needs to be 298K, while the duration of mechanical activation needs to be less than 5min. After longer mechanical activation, the mixtures are prone to bulk combustion even at low initial temperatures. Single-phase (Ta,Zr)C carbide with the lattice parameter of 0.4479nm was synthesized by forced SHS compaction in a sand mold.