The thesis is devoted to the development of brazing filler metal for brazing perspective materials based on aluminide nickel, which does not contain boron, silicon and technological process of high temperature vacuum brazing.
The results of investigations of temperature melting intervals, filler metal microstructure on the basis of Pd-Ni-(Me)-Ge, Ni-Cr-Nb and Ni-Cr-Co-Mo-W-Al-Ti-Nb systems are given. The liquid waste of experimental filler metal temperature is in the range of 1186...1261 ˚С, which does not exceed the temperature threshold of stability of aluminide of nickel Ni3Al (γ'-phase).
Experimental research has established the influence of niobium and titanium on the melting point of experimental nickel based filler metal, and the surface of a liquid filler metal of a multicomponent filler metal has been constructed. It has been established that the use of titanium and niobium in a multi-component nickel-based filler metal makes it possible to obtain a melting temperature in the range of 1240...1261 ˚С. The formation of the structure of brazing joints from the alloy on the basis of nickel alumina obtained with the use filler metal of various doping systems has been investigated.
The influence of temperature on the magnitude of the wetting angle during the dispersion of the Ni-Co-Ti-Nb-Cr-W-Al-Mo filler metal on the substrates of Ni3Al
based heat-resisting nickel alloy was investigated. It was established that the marginal angle of wetting decreases with temperature rise from 1245˚С to 1280˚С from 14˚ to 12˚, which testifies to good wetting of the base metal.As the temperature increases, the depth of penetration of filler metal into the main material from 104.23 to 343.94 microns.
It has been established that the corrosion resistance of filler metal after spreading on the base metal improves, the corrosion potential moves to the electropositive region, which is due to mutual diffusion processes on the interphase boundary of the particles - the main metal.
The mechanism of the formation of the brazing seam in alloy compounds based on nickel alumina obtained using filler metal based on palladium is established. Local microrentense spectroscopy analysis revealed that in the brazing seam the formation in center eutectics enriched with aluminum is observed, which leads to the sparkling of the brazing connection and obtaining low strength.
The mechanical properties of brazing joints at elevated temperature were studied and long-term durability was studied in conditions of constantly acting load at high temperature.
On the basis of the research results, a multicomponent filler metal were created on the basis of nickel Ni≥25 (Cr, Co, Mo, W) ≥20 (Al, Ti, Nb) - (1-5) Zr; Ni≥25 (Cr, Co, Mo, W) ≥20 (Al, Ti) ≥15 Nb and the technological process of high temperature vacuum brazing, which provides high short and long term durability (210...220 hours) at a temperature of 900 °C and constantly operating load of 150 MPa.
Established as a condition for increasing the long-term strength of brazing nickel aluminide compounds under conditions of a constant load of 150 MPa and a temperature up to 900 ˚С is the formation of a structure containing phases characteristic of the base metal in a brazing seam – Ni3Al (7,93 % Al) and NiAl, (5,74 % Al).
The developed multicomponent filler metal and brazing technology on the basis aluminide of nickel can be used effectively when brazing and repairing defects in casting of parts, which are operated under high temperature conditions and constantly operating loads.
