Analyzing metallurgical interaction during arc surfacing of barrier layers on titanium to prevent the formation of intermetallics in titanium-steel compounds

This paper considers a possibility to obtain high-quality butt junctions of bimetallic sheets from steel clad with a layer of titanium, with the use of barrier layers. The task that was tackled related to preventing the formation of Ti-Fe intermetallic phases (IMPs) between the steel and titanium layer. The barrier layers (height ~0.5 mm) of vanadium and copper alloys were surfaced by arc techniques while minimizing the level of thermal influence on the base metal. To this end, plasma surfacing with a current-driving wire and pulsed MAG surfacing were used. The obtained samples were examined by methods of metallography, X-ray spectral microanalysis, durometric analysis. It has been established that when a layer of vanadium is plated on the surface of titanium, a defect-free structure of variable composition (53.87–65.67) wt % Ti with (33.93–45.54) wt % V is formed without IMPs. The subsequent surfacing of steel on a layer of vanadium leads to the formation of eutectics (hardness up to 5,523 MPa) in the fusion zone, as well as to the evolution of cracks. To prevent the formation of IMPs, a layer of bronze CuBe2 was deposited on the surface of vanadium. The formed layer contributed to the formation of a grid of hot cracks. In the titanium-vanadium-copper transition zones (0.1–0.2 mm wide), a fragile phase was observed. To eliminate this drawback, the bronze CuBe2 was replaced with bronze CuSi3Mn1; a defect-free junction was obtained. When using a barrier layer with CuSi3Mn1, a defect-free junction was obtained (10–30 % Ti; 18–50 % Fe; 5–25 % Cu). The study reported here makes it possible to recommend CuSi3Mn1 as a barrier layer for welding bimetallic sheets "steel-titanium". One of the applications of the research results could be welding of longitudinally welded pipes of main oil and gas pipelines formed from bimetallic sheets of steel clad with titanium.

Виготовлення авіаційних деталей з жароміцних нікелевих сплавів методом адитивного плазмового наплавлення

The aviation part of the ring-type was made of heat-resistant structural alloy EI 868 (HN60VT) by the method of additive multilayer plasma surfacing with wire. The traditional technology for obtaining this type of ring blank is the stamping of rods, which are then brought to the final shape of the part by further machining. The disadvantage of traditional technology is the significant cost of metal, which in the process of machining the pressed rod, is converted into chips and not reused, which increases the cost of the finished product. The use of additive technologies will significantly reduce the cost of material in obtaining annular workpieces by manufacturing a workpiece with a configuration as close as possible to the geometry of the part. Additive surfacing was performed on a robotic complex consisting of a plasma power supply SBI PMI-350 AC/DC TL and work FANUC M-710iC on a rigidly fixed substrate of steel 20. To determine the possibility of obtaining aviation parts using the method of layer-by-layer plasma surfacing, a study of the deposited material was conducted The structure of the grown part was studied, it was found that the microstructure corresponds to the normal state of the alloy EI868 (HN60W) in the microstructure of the fusion line is not visible, the structure is homogeneous with the mutual germination of grains between layers. Alloy parts obtained using the method of additive cultivation are at the level of cast blanks and forgings and at T = 900oC are: sв =35±5 кгс/мм2,s0,2 =49±5 кгс/мм2, y = 62±5 %. After machining the grown workpiece, a capillary method of control and radiation control of the grown part - cracks and other types of critical metallurgical defects was not detected. The practical significance of the introduction of this method is a significant reduction in material costs in obtaining parts and ensuring economic efficiency, which is about 159 thousand hryvnias.

Comparing features in metallurgical interaction when applying different techniques of arc and plasma surfacing of steel wire on titanium

This paper reports a study into the regularities of interphase interaction, features in the formation of intermetallic phases (IMPs), and defects when surfacing steel on titanium in four ways: P-MAG, CMT, plasma surfacing by an indirect arc with conductive wire, and PAW. A general tendency has been established in the IMP occurrence when surfacing steel on titanium by all the considered methods. It was determined that the plasma surfacing technique involving an indirect arc with conductive wire is less critical as regards the IMP formation. That makes it possible to obtain an intermetallic layer of the minimum thickness (25...54 μm) in combination with the best quality in the formation of surfaced metal beads. Further minimization of the size of this layer is complicated by a critical decrease in the heat input into the metal, which gives rise to the capability of the surfaced metal to be collected in separate droplets. The formation of TiFe2, TiFe, and the α-Fe phase enriched with titanium in different percentage compositions has been observed in the transition zone of steel surfacing on titanium under different techniques and modes of surfacing. The study has shown the possibility of formation, in addition to the phases of TiFe2 and TiFe, the Ti2Fe phase at low heat input. The technique of plasma surfacing by an indirect arc with conductive wire minimizes the thermal effect on the base metal. When it is used at the border of the transition of the layer of steel surfaced on titanium, the phase composition and structure of the layers in some cases approach the composition and structure of the transition zone of the original bimetallic sheet "titanium-steel" manufactured by rolling. A layer up to 5 μm thick is formed from the β phase with an iron concentration of 44.65 % by weight and an intermetallic layer up to 0.2...0.4 μm thick, close in composition to the TiFe phase. The next step in minimizing the IMP formation might involve the introduction of a barrier layer between titanium and steel.

Distribution on microhardness, chemical composition and structure over a layer of heat-resistant highyardness alloy formed by multilayer plasma surfacing in a nitrogen medium

Microhardness distributions, surface morphology, and elemental composition of a deposited layer of a heat-resistant alloy of the type P2M8U steel formed by plasma surfacing in a protective-alloying nitrogen medium are studied. It was established that the surfacing technology and surfacing material allows to obtain a high-quality deposited alloy without cracks, pores, slag inclusions and defects of macro- and microstructure. It has been established that the deposited material is pearlite grains at the boundaries and grain junctions of which are carbonitrides based on iron, tungsten, chromium, molybdenum, aluminum (Fe6 W6 NC and AlN).