Polycrystalline cubic boron nitride sintered with Ti(C,N)-W-Al mechanically alloyed binders

The structural changes in Ti(C,N)-W-Al mechanically alloyed (MA) binders and the sintering mechanism of PcBN were investigated by XRD, SEM and TEM techniques. The elastic properties of PcBN compacted were determined by ultrasound technique. Tungsten was efficiently dissolved in Ti(C,N) by mechanical alloying, forming homogeneous binders during sintering. Opposite strain effects were induced in the binders than in PcBN particles. Dissolution of W in Ti(C,N) enhanced the fracturing of the cBN particles and the formation of the nanostructured binder pools by increasing the hardness of binder particles. Poisson's ratios and Young's moduli of the new PcBN products were higher than the reference product. Micro-Vickers hardness of sintered products increased with milling time of the binder powder. Slightly higher hardness values were achieved when Al powder was mechanically alloyed with Ti(C,N) and W powders than when it was attrition milled with MA Ti(C,N)-W.     

The design of advanced performance high strength low-carbon martensitic armour steels: Microstructural considerations

Neither a higher hardness nor higher mechanical properties (yield strength, ultimate tensile strength, impact energy, and %elongation) appear to be exclusive or even reliable criteria for predicting the ballistic performance of martensitic armour steels, as shown in our previous work [K. Maweja, W.E. Stumpf, Mater. Sci. Eng. A (February), submitted for publication]. An alternative design methodology for tempered martensitic armour steels is, therefore, proposed which is based on the effect of retained austenite on the ratio of the yield to ultimate tensile strength (YS/UTS), the microstructure of the tempered martensite and its martensite start temperature M_s. This approach was developed using 6 mm thick armour plates and later was successfully applied to the design of eight experimental armour steels with plate thicknesses ranging from 4.7 to 5.2 mm and tested by the standard R4 (5.56 mm rounds) ballistic test.     

Regulated rivers in Zambia—The case study of the Kafue river

Until today, the majority of the Zambian rivers have been able to keep their natural character. Impoundment has been the principal measure carried out so far. The Kafue River is the most important waterway for the national economy. Its middle and lower sections are regulated by the Itezhi-tezhi and Kafue Gorge Reservoirs. The changes in the natural flow pattern have threatened the ecological equilibrium of the Kafue Flats. Conductivity, concentration of sulphates and chlorides are reduced in the regulated section.     

Effect of pressure and treatment temperature on the structural evolution of mechanically alloyed Ti(W)(C,N)–Al admixes in boron nitride

The effect of pressure and temperature on the structural changes of admixtures of cBN, Al and Ti(C_0.5N_0.05) or Ti(C_0.5N_0.5)_0.6 mechanically alloyed powders with 40 mass% W were investigated by means of the X-ray diffraction technique. It emerged that pressure and temperature affected the crystal structures and compositions of the binder phases as well as the behaviour of the contaminating Fe. High pressure–high temperature (HPHT) sintering favoured the formation of Ti(W,Al)(C,N) solid-solutions, whereas vacuum annealing favoured the formation of W(Ti,Al) solid-solutions. Products of Ti(C,N)-based crystal lattices remained stable under high pressure (5 GPa), whereas W based crystal lattices were more stable under vacuum (0.001 Pa). Inert single phase binders were formed in HPHT sintered PcBN compacts. Formation of Ti(W,Al)(C,N) by reactions between mechanical alloyed Ti(W)(C,N) powder particles and liquid Al prevented the formation of AlN, AlB₂, α-AlB₁₂, TiN and TiB₂ particles in PcBN compacts. Sintering of PcBN occurred by dissolution of B and N atoms in Ti(W,Al)(C,N) and re-precipitation on cBN particles.     

Thermal stability and magnetic saturation of annealed nickel-tungsten and tungsten milled powders

Crystal structures, microstructures and magnetic saturation of annealed pure W powder along with W-40 wt.% Ni powder mixtures processed by high-energy ball milling were investigated using XRD, DTA, SEM and saturation magnetization techniques. Thermally induced transformations occurred at low temperature annealing. Supersaturated metastable Ni(W) solid solution formed during mechanical milling decomposed during annealing treatment into FCC Ni-rich, FCC W-rich phases and an eta-type phase which was constituted of BCC lattice of W enveloped by two FCC lattices of Ni and W. The structures of the major annealing products were close to Ni₁₀W and W₃Ni₂. The magnetic saturation of the milled W powder and W-Ni mixtures decreased with the increase in annealing temperature. Milling time was more influential on the magnetic properties of the annealed pure W powders.     

Microstructure and crystal structure of an equimolar Mg-Ti alloy processed by Simoloyer high-energy ball mill

The solid solubility of 50-50 at.% Mg-Ti powder mixtures was achieved by means of high energy ball milling in a Simoloyer equipment. XRD and HRTEM analyses revealed the existence of FCC and BCC matrix of Ti solid solution in Mg containing small amounts of an HCP Ti-rich phase formed after milling for 48 and 72 h, respectively at 800 rpm. An intermediate FCC solid solution of Ti in Mg was identified in powders milled for 24 h or less. The chemical composition of the matrix products extended from Ti56:Mg44 to Ti50:Mg50, which is close to the targeted equimolar ratio. XRD analysis of the structure suggested that the release of the lattice strain energy contributed to the driving force for transformation and solid solution between Mg and Ti after ball milling. Twinning was observed in Ti-rich crystallites at intermediate milling time. The twinning observed could be attributed to the deformation of Ti particles. However, in the Mg-Ti system, it might also indicate a strain induced martensitic transformation of the metastable ω-FCC into BCC product. The crystallite boundaries acted as preferential sites for the heterogeneous nucleation of the twins and for the formation of solid solution by release of the lattice strain energy.     

Cleaning of a copper matte smelting slag from a water-jacket furnace by direct reduction of heavy metals

Cleaning experiments of a copper matte smelting slag from the water-jacket furnace was undertaken by direct reduction in a laboratory-scale electric furnace. The effects of coal-to-slag ratio, w, and the reduction time, t, were considered for two different coal/slag mixing procedures. In the first procedure, metallurgical coal was added to the molten slag, whereas in the second procedure, coal was premixed with the solid slag before charging into the furnace. The recovery of heavy metals (Cu, Co), and the fuming of Pb and Zn were investigated. Contamination of the metal phase by iron and the acidity index of the final slag were analysed as these may impede the economical viability of the process. The lower w value of 2.56% yielded a recovery rate of less than 60% for copper and less than 50% for cobalt, and around 70% for zinc. However, increasing w to 5% allowed the recovery of 70-90% for Cu, Co and Zn simultaneously after 30-60 min reduction of the molten slag. After reduction, the cleaned slags contained only small amounts of copper and cobalt (<0.4 wt%). Fuming of lead and zinc was efficient as the %Pb of the residual slag dropped to levels lower than 0.04% after 30 min of reduction. Ninety percent of the lead was removed from the initial slag and collected in the dusts. The zinc content of the cleaned slags quickly dropped to between 1 and 3 wt% from the initial 8.2% after 30 min reduction for w value of 5 and after 60 min reduction for w value of 2.56. The dusts contained about 60% Zn and 10% Pb. Recovery of lead from fuming of the slag was higher than 90% in all the experimental conditions considered in this study.     

Effects of tungsten and aluminium on the oxidation and phase formation in mechanically alloyed Ti(C,N)–W–Al systems

The effects of milling parameters and composition of the powder mixtures on the transformations of Ti(C,N)–W–Al powders processed by high energy ball milling were investigated by XRD, SEM and TEM. The strain energy and the fine particle size contributed to the high chemical reactivity with oxygen of the powders milled for 12–24 h. Powders milled for 48 h were chemically stable. The affinity with oxygen decreased after W dissolution in Ti(C,N), and the subsequent decrease in lattice strains. Aluminium lowered the lattice strains, and subsequently the strain energy stored in the deformed crystals of Ti(C_0.5N_0.05) and W milled above 25 °C. Fracturing of hard particles dominated in the early stage of milling in the absence of Al, whereas with Al, plastic deformation of particles and cold welding of Ti(C,N) and W particles by the softer Al prevailed at the same time.     

Transformation and alloying mechanisms in sub-stoichiometric titanium carbonitrides - tungsten high energy ball milled powders

The transformations occurring in the sub-stoichiometric Ti(C,N) - W system processed by high energy ball mill were investigated. The transformation stages and mechanisms of alloying are discussed with respect to the changes in crystal structures of the powder constituents. The milling atmosphere had an effect on the lattice strain of milled products, and hence on the kinetics of solid state dissolution between the powder constituents, but it did not affect the fracturing process. The release of the stored crystallite lattice strain energy was the major determinant in mechanical alloying, with particle size reduction playing a necessary, but less significant role.     

Annealing behaviour of sub-stoichiometric Ti(C,N)-W mechanical alloy powders

The annealing behaviour of Ti(C_0.5N_0.05)-40 wt.% W and Ti(C_0.5N_0.5)_0.6-40 wt.% W mechanically alloyed powders was investigated using XRD, TEM, SEM and DTA techniques. It was observed that the reaction start and finish temperatures between constituents were lower in the system that had higher residual lattice strains after milling. The compositions of the intermetallic compounds and solution phases formed were dependent of the milling conditions and the annealing temperature. Thermal alloying was observed during annealing of Ti(C_0.5N_0.05)-40 wt.% W mechanically alloyed products, whereas de-mixing of W-rich phases from the metastable solid solution occurred during annealing of the Ti(C_0.5N_0.5)_0.6-40 wt.% W milled powders.