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doi: 10.1007/BF02469092pmid: N/A
1. High-temperature steels and alloys fracture in soldering by a brittle mechanism (this is the most typical for dispersion-hardening alloys). 2. An elevated sensitivity of dispersion-hardening alloys to the action of molten solder is observed in a specific temperature range where their plasticity falls abruptly upon heating. 3. In soldering structures by copper-silver solders, such factors as the multiphase structure, the grain sized>0.1 mm, the duration of contact with the melt, the hydrogen content exceeding 3×10−4 wt.%, the low-melting elements Pb, S, and Sn, the mechanical strength concentrators (sealing flanges), and the growth of the deformation rate enhance the embrittlement of the materials, whereas a barrier coating possessing a chemical affinity for the solder weakens it. The scale factor virtually does not affect the degree of embrittlement. 4. Upon the interaction between the material and the molten melt, the overstress and the rate of fracture become enhanced and the activation energy and the fracture toughness diminish. These changes are more typical for dispersion-hardening alloys than for steels and homogeneous alloys.
doi: 10.1007/BF02469093pmid: N/A
1. The inhomogeneity of the chemical composition that appears in steel on the boundary with the soldered joint markedly worsens the strength of the soldered joint. 2. In order to prevent early fracture of the soldered structure, we developed theoretical and experimental substantiation for designing the soldering process, which consists of allowance for the special features of the design of the structure and the mechanical, thermophysical, and rheological properties of the materials and the solder.
doi: 10.1007/BF02469094pmid: N/A
1. Cracks that appear in soldering materials of different kind are a result of the simultaneous action of the appearing tensile stresses and the solder melt. 2. The appearance of tensile stresses in soldering is connected with the volume changes; in alloy ÉP202 they are caused by intensification of the decomposition of the solid solution accompanied by the segregation of particles of fine disperse phases and in steel VNS16 they are caused by the segregation of particles of carbide phases and the α→γ transformation. In addition, the appearance of stresses in a specific temperature range is promoted by technological factors, coarse grains, the deformation rate, the presence of hydrogen, etc. 3. The tensile stresses intensify the decomposition of the solid solution accompanied by segregation of hardening phases and their coarsening, especially over grain boundaries. 4. A crack appearing in materials during soldering has a wedge shape and a sharp notch in the frontal plane; its growth has an intercrystalline nature. The propagating cracks branch due to the pores and cracks appearing in the volume of the metal. 5. The growth of cracks in soldering occurs from the surface and in the bulk of the material. The growth of a crack from the surface is characterized by jumps due to the repeated processes of accumulation and consumption of elastic energy at the tip of the crack when it propagates and stops respectively. 6. Corrosion and diffusion processes develop in the zone of surface cracks. The corrosion process is characterized by selective dissolution of nickel, which forms the base of alloy ÉP202 and is an alloying element in steel VNS16, in the liquid solder. The diffusion process is characterized by predominant penetration of copper into the lattice of the materials. Corrosion and diffusion are not observed in fracture zones in the bulk of the specimens.
doi: 10.1007/BF02469095pmid: N/A
1. Brittle fracture and the decrease in the strength of materials under the action of molten solder are connected with the marked decrease in their plasticity caused by the intensification of the decomposition of the solid solution with segregation of particles of hardening phases in the alloys supplemented with a α→γ transformation in the steels. 2. The enhancement of the sensitivity to embrittlement in specimens with a stress concentrator (a notch) or with coarse grains in contact with molten solder is due to the intensification of the processes connected with the appearance of stresses and inhibition of plastic deformation. In the presence of coarse grains this is also connected with the elevation of the density of segregations over grain boundaries (the total length of grain boundaries decreases).
Derkach, G.; Zheleznyak, O.; Pestov, Yu.; Semenov, V.
doi: 10.1007/BF02469096pmid: N/A
1. The mechanical properties, the microstructure, and the phase composition of steel 07Kh16N6 with different contents of carbon after a heat treatment simulating the production process of a part from steel 07Kh16N6 and granulated nickel alloy ÉP741NP joined by the method of HIP fully recover the optimum values after the final heat treatment by a regime recommended for steel 07Kh16N6. The mechanical properties of alloy ÉP741NP do not worsen. 2. Counter diffusion of Fe, Cr, and C from the steel into the alloy and of Ti, Al, Nb, W, and Mo from the alloy into the steel is observed in the diffusion zone of the combined preform. A narrow (15–20 μm) carbide zone with an elevated concentration of titanium is formed due to the counter diffusion over granule boundaries of alloy ÉP741NP. The depth of iron diffusion into alloy ÉP741NP is 40–50 μm. 3. The mechanical properties of the combined preform at a temperature ranging from −196 to +650°C are close to the properties of steel 07Kh16N6; fracture occurs predominantly over the diffusion zone. 4. In order to raise the working capacity and reliability of units with rotating parts from alloy ÉP741NP joined permanently to a shaft from steel 07Kh16N6 by the method of HIP, the shaft should be coated with a nickel barrier layer that diminishes the possibility of the formation of titanium carbide on the surface of alloy ÉP741NP over granule boundaries.
Pestov, Yu.; Zheleznyak, O.; Derkach, G.; Semenov, V.
doi: 10.1007/BF02469097pmid: N/A
1. The changed surface layer formed on a compact of alloy ÉP741NP due to the interaction with the metal of the capsule (steel 20) in the process of hot isostatic pressing and subsequent heat treatment is enriched with iron and carbon and depleted of nickel and cobalt. 2. The changed surface layer 200–300 μm thick on specimens of alloy ÉP741NP diminishes the fatigue resistance of the alloy by 15% (650 MPa against the original 750 MPa) in testing at 20°C, but does not embrittle the material and does not initiate fatigue fracture or influence the fracture behavior.
Zheleznyak, O.; Semenov, V.; Kozykov, B.; Derkach, G.; Nedashkovskii, K.; Zaitsev, M.; Nikolaev, A.; Revina, N.; Movchan, Yu.
doi: 10.1007/BF02469098pmid: N/A
1. The developed regimes of hot deformation and nonstandard heat treatment of large rolled rings up to 500 mm in diameter from rods 100 mm in diameter made of beryllium bronze BrB2 provide a high rupture strength (μr > 1000 MPa) and an elevated ductility (δ>6%, ψ>11%) and impact toughness (KCV>120 kJ/m2). 2. The created technology prevents the appearance of hot cracks, eliminates repeated heat-treatment operations, increases the yeild, and gives preforms with a homogeneous fine-grained structure and stable mechanical properties, which provides reliable service in sealing parts operating in the elastoplastic range in superduty units of liquid-propellant rocket engines.
Seliverstov, D.; Samarov, V.; Kratt, E.; Derkach, G.; Pestov, Yu.; Zheleznyak, O.; Zaitsev, M.; Semenov, V.
doi: 10.1007/BF02469099pmid: N/A
1. We have managed to fabricate a part with a high geometrical precision of passages after creating a unique experimental model. 2. For the first time in the production of turbine wheels we have designed components without using the paper technology, using as a basis - computer processing of the specified geometry of the flow part and its representation as a system of virtual surfaces; - three-dimensional simulation of the variation of the capsule shape in HIP and generation of a data file for plotting the surfaces of net shape components; - processing of the data in a computer-aided design system followed by three-dimensional breadboarding of the net shape components; - development of control software and data files for the production of net shape components in multi-coordinate N/C machines. 3. Powder metallurgy based on the HIP process makes it possible to widen the traditional framework of the production of parts with a complex configuration. The HIP process of such parts complemented with advanced concepts and methods of computer simulation and material science is indeed an effective means for creating superduty units and components from promising hard-to-shape materials.
doi: 10.1007/BF02469100pmid: N/A
1. The elevated content of silicon in high-carbon, chromium-manganese alloys increases the wear resistance only if the content of carbon and manganese in them is sufficiently high and the structure is oriented. 2. The introduction of about 4% Si into high-carbon chromium-manganese alloys increases their wear resistance by 60% or doubles it with respect to the most expensive alloy sormite-1
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