Papers by Keyword: Dispersion Hardening

Abstract: The peculiarities of the microstructure and properties of BrBNT1.7 beryllium bronze tape samples were studied: the samples were subjected to dispersion hardening as a result of quenching in a supersaturated solid solution and aging. Friction deformation in a dry friction mode provides additional effective hardening while maintaining increased plasticity (bending-and-unbending test).

Abstract: The effect of tungsten nanoparticles and microparticles on the structure and hardness of sintered Sn–Cu–Co–W alloys has been studied. Tungsten powder of 19–24 μm sized particles was milled in a planetary-centrifugal mill, after which the size of particles was 25 nm to 20 μm. The milled and non-milled tungsten was then mixed with powders of tin, copper and cobalt. The specimens were compacted in moulds and sintered in vacuum at 820°C for 20 minutes. The structure of sintered materials was studied using X-ray diffraction analysis and scanning electron microscopy. Microhardness (HV_0.01) of structural constituents and hardness of the materials were measured. It has been determined that it is alloys containing mechanically milled tungsten that have the highest hardness. The main factor influencing the rise of hardness is dispersion hardening with nanoparticles. A further factor is work hardening of tungsten microparticles during ball milling. The highest hardness of 109–111 HRB has been obtained in the Sn–Cu–Co–W alloy containing 23% wt. of milled tungsten, with the proportion of tin, copper and cobalt being 1/2.6/1.6.

Abstract: In this article, the microstructural peculiarities and properties of dispersion-hardened beryllium bronze with Ni and Ti are studied after quenching (780 °C) in a supersaturated solid solution and aging (320 °C, 3h). Decomposition of the α-solid solution matrix is implemented by means of an intermittent reaction with a primary allocation intermetallic χ-phase (type Be₁₂Ti) with a VCT-lattice. It is shown that the strength properties (yield strength, micro-hardness) of the alloy more than double after aging.

Abstract: The scientific bases for the development of rational compositions and methods for hardening a large-sized metallurgical tool from micro-alloyed steels are stated. Based on the generalization of the experimental data, the regularities of phase and structural transformations at various stages of the technological cycle are revealed; the relationships between structural parameters, chemical composition and mechanical properties have been studied and described.

Abstract: Macroscopic mechanical responses of alloy steels dispersed with fine vanadium carbide particles [1] were analyzed by crystal plasticity finite element method. Average distance of dispersed particles was used as a microscopic length scale and introduced to the models of the critical resolved shear stress and the mean free path of dislocations. Numerical result of yield stress agreed well with that of experimental result [1], but that of the work hardening rate was slightly higher than that of experimental one. When the dislocation mean free path was set to be 2 to 3 times the average spacing of dispersed particles, the work hardening rate fit better with the experimental one.

Abstract: Plastic deformation and dislocations accumulation in a steel alloy dispersed with vanadium carbide particles is numerically analyzed by a crystal plasticity finite element technique and work hardening characteristics are discussed. Increment of dislocation density that contributes to work hardening is calculated from the mean free path of dislocations. The mean free path is defined by the spacing of forest dislocations and the average spacing of dispersed particles. Obtained yield stress and work hardening characteristics was close to that of experimental result, except that the value of work hardening rate was higher than that of experimental one.

Abstract: The structural changes and the strengthening of a Cu-3%Ag alloy subjected to large strain drawing and subsequent annealing were studied. The cold working was carried out at an ambient temperature up to total strain above 8. The hardness increased from 600 MPa in the initial state to about 1800 MPa with increasing the total strain. The annealing treatment at 400°C resulted in increase in the hardness to about 2000 MPa for the samples cold worked to total strains above 2. On the other hand, the hardness change of the samples annealed at 450°C dependent significantly on the preceding cold strain. Namely, annealing softening took place in the samples processed to strains below 5, while the samples processed to larger strains were characterized by remarkable hardening after annealing. The value of annealing hardening increased with increasing the previous cold strain, leading the hardness to 2500 MPa in the sample strained to 7.4. The cold worked and annealed samples were characterized by the development of lamella-type microstructure consisting of highly elongated copper grains with uniform distribution of nano-scaled silver particles having a size of about 2 nm.

Abstract: Surface alloys with composition ranging from 10 to 20% Cr were produced by laser surface alloying. Their microstructure consists of faceted plate-like Al4Cr intermetallic compound particles dispersed in a matrix of α-Al solid solution. During remelting, heterogeneous nucleation of eutectic Al7Cr/α-Al occurred in the undercooled liquid ahead of the columnar solid-liquid interface, followed by equiaxial solidification, resulting in a microstructure formed of equiaxed cells. Al-Cr alloys present Young’s modulus and hardness values that increase with increasing volume fraction of intermetallic compounds. Wear resistance, measured in dry sliding conditions, increases with increasing load due to the protective effect of a stable mechanically mixed layer that forms at the surface of the samples and the steel counterbody. Alloys formed of equiaxed eutectic cells provide better wear resistance than those formed of large plate-like particles since a thinner, more stable and harder mechanically mixed layer is formed, which offers best protection against wear.