Lilia I. Shevtsova

Influence of the explosively welded composites structure on the diffusion processes occurring during annealing

Currently layered composites with intermetallic interlayers are promising materials for many industries. Materials of this type involve composites consisting of titanium and titanium aluminides layers. One of the methods of such composites fabrication is explosive welding and annealing. In this paper the structure and properties of explosively welded multilayered composites is described. Structural studies were carried out by the methods of optical metallography, scanning and transmission electron microscopy. The properties of local zones of material were estimated by the measuring of a microhardness level. The explosive welding process accompanied by the structural changes of material adjacent to “Al-Ti” interfaces. The structural investigation revealed the formation of several areas: vortex zones, which are characterized by aluminum and titanium mixing, and severely deformed areas. These structural features have the strong influence on the diffusion processes occurring during annealing of composites. The most intensive diffusion was observed in the welded joints where the most significant structural changes occurred. It was identified that Al3Ti is only one phase which forms during heat treatment of “Ti-Al” composites. The main conditions of “Ti-Al3Ti” composites fabrication are the correct choice of aluminum and titanium plates thickness and optimal conditions of heat treatment.

Flaw inspection of welded joints in titanium alloys by the eddy current method

Abstract The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.

Surface Hardening of Steel by Electron-Beam Cladding of Ti+С and Ti+B4C Powder Compositions at Air Atmosphere

Structural investigations of the materials obtained by surface alloying with titanium-containing powder compositions using industrial electron acceleration were carried out. It was revealed that hardened particles of titanium carbides and borides were formed as a result of high-energy treatment. The highest value of materials studied microhardness was about 8.4 GPa. Friction testing against fixed abrasive particles showed that electron-beam cladding of the titanium and graphite mixture conduced to increasing material wear resistance by a factor of three.

Spark Plasma Sintering of Mechanically Activated Ni and Al Nanopowders

The structure and mechanical properties of materials fabricated by spark plasma sintering of mechanically activated mixture of nickel and aluminum nanopowders were investigated. On account of the elemental powders ratio formation of Ni3Al compound was expected. Relative density of sintered samples was equal to ~ 95 %, microhardness of materials was 6540 MPa. Ultimate tensile strength of samples tested according to three-point bending scheme exceed 1100 MPa.

Boron-modified Ni3Al intermetallic compound formed by spark plasma sintering of mechanically activated Ni and Al powders

A Ni3Al intermetallic compound was obtained by spark plasma sintering of mechanically activated Ni and Al powders in atomic ratio 3:1 respectively. Samples with boron addition of 0.1 and 0.2% (wt.) and samples without boron were obtained. The maximum value of the relative density (~99 %) has been obtained for the material by sintering of mechanically activated mixture powders modified with 0.1% of boron. No differences have been found between the structure of boron-modified Ni3Al and Ni3Al without boron addition. The maximum level of bending strength (2200 MPa) has been achieved for Ni3Al with 0.1% (wt.) of boron. This value is almost 3 times the bending strength of the sample of Ni3Al sintered without boron addition.

Subminiature eddy current transducers for studying semiconductor material

Based on an eddy-current transducer (ECT), a probe has been designed to study the semiconductor material. The structural diagram of the probe is given and the basic technical data are stated (the number of windings is 10-130 turns, and the value of the initial permeability of the core μ max = 500). Due to the high confinement of the magnetic field, it is possible to acquire data from small areas of semiconductor plates. Response versus ECT positioning diagram is also provided.

Effect of Plastic Deformation of the Initial Components and Particle Size Reduction on the Structure and Properties of the PN85YU15-Ni Composite Material Produced by Spark Plasma Sintering

Structure and mechanical properties of the PN85YU15 - Ni composite materials obtained by spark plasma sintering were investigated. Two types of powder mixtures, namely, nickel mixed with coarse-grained nickel aluminide and nickel mixed with fine-grained nickel aluminide were used to obtain the composites. Nickel aluminide and nickel powders were taken in the ratio 7:3 respectively. The effect of the initial nickel aluminide particle sizes and plastic deformation due to the ball milling on the structure and mechanical properties of materials sintered at 1100 °C and pressure of 40 MPa was determined. Plastic deformation and refining the initial intermetallic powder particle sizes leads to increasing the sintered material relative density to 95%. The tensile strength of the PN85YU15-Ni composite material obtained by sintering of the milled PN85YU15 powder and nickel in the ratio 7:3 was 1060 MPa. This value is almost twice as high as the tensile strength of the composite containing a no significant plastic deformed coarse-grained intermetallic compound powder (590 MPa), and three times higher than the tensile strength of the sintered nickel aluminide powder (380 MPa).

Formation of Sintered “PN85Yu15 – Ni” Powder Composites by Using the SPS Method

PN85U15 - Ni composites were obtained by spark plasma sintering (SPS) of the powder mixture consisted of nickel and nickel aluminide. Particular attention in this study was focused on the discussion of the problem concerning the influence of the nickel content on mechanical properties of the sintered composites. The microstructure of the sintered materials consisted of spherical intermetallic particles homogeneously distributed in the nickel matrix. The relative density of all sintered materials was higher than 90 %. The hardness of the fabricated composites decreased from 3100 MPa (PN85U15 sintered powder) to 2500 MPa (70 % PN85U15 with 30 % Ni). It was found that the PN85U15 – Ni composite containing approximately 30 wt. % of Ni possessed the highest bending strength (1900 MPa).

The Effect of Preliminary Mechanical Activation on the Structure and Mechanical Properties of Ni3Al+B Material Obtained by SPS

In the present study, a mixture of powders (87.9 at.% Ni, 12 at.% Al, 0.1 at.% B) was used as the initial material to produce sintered Ni3Al + B alloy. Spark Plasma Sintering (SPS) method was used to compact the powder. The powder mixtures were previously prepared in two ways: mixing the initial powders in a mortar (М1) and mechanical activation (М2). The microstructure was observed using optical microscope (OM). The addition of small amount of boron to the initial mixture of nickel and aluminum improves the density of the sintered Ni3Al intermetallic compound (98.8%). The results of density, bending and microhardness tests showed, that the provisional three-minute mechanical activation improves almost all properties of the sintered material. The compact obtained by SPS by M2 contributes to the formation of a homogeneous fine-grained structure of the material. It leads to further increase in flexural bending strength up to 2200 MPa. This value is almost 8 times the strength of the intermetallic Ni3Al stoichiometric composition obtained by SPS.

Non-destructive testing of nanomaterials by using subminiature eddy current transducers

A sensor for studying nanomaterials has been developed on the basis of a transformer-type eddy-current transducer. The basic technical data are stated (the number of windings is 100-400 turns, and the value of the initial permeability of the core is µmax = 36000). Measurements technique which allows high-precision measuring the electrical conductivity in thin film Ce-Nb. The electrical conductivity of Niobium-Selenium varies from 3.3105 to 3.7105 MS/m in the ratio of four from 4 to 60 nm.