Cesium vapor source based on gas-regulated heat pipe for an autonomous thermionic egc

The results of work on the development of a source of cesium vapor for a thermionic EGC based on a gasregulated heat pipe and investigations of its basic technical characteristics in the cesium vapor range 30–700 Pa are presented. It is shown that the evacuation capacity and zero response time of a gas-regulated heat pipe based vapor source and the possibility of continuously monitoring the cesium vapor pressure via the temperature in the adiabatic zone and the pressure in the gas reservoir are all effective.     

Superplastic ductility of oxide and nonoxide ceramics

The superplastic ductility of oxide and nonoxide SHS ceramics is considered. It is established that with certain temperature-rate dependences these ceramic materials manifest features typical of superplastic flow. It is shown that the ceramics undergo some specific microstructural changes under strain conditions.Institute of Problems of Metal Superductility, Russian Academy of Sciences, Ufa. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 617–622, November, 1993.     

Effect of deformation temperature on microstructure evolution in aluminum alloy 2219 during hot ECAP

The effect of deformation temperature on microstructure evolution during equal channel angular pressing (ECAP) was studied in a coarse-grained aluminum alloy 2219 in a wide temperature interval from 250 to 475 °C. The structural changes taking place during ECAP up to strains of 12 are classified into the following three stages irrespective of deformation temperatures: i.e. (1) an incubation period for formation of the embryos of deformation bands (DBs) at low strains; (2) development of large-scale DBs followed by grain fragmentation at moderate strains; (3) rapid development of new grain at high strains. Microstructure development in stages 1 and 2 is hardly influenced by temperature, while that in stage 3 is most significantly affected at higher temperature. An increase in the pressing temperature leads to decreasing the volume fraction of new grains and increasing the average grain size in stage 3. This can be attributed to relaxation of strain compatibility between grains due to frequent operation of dynamic recovery and grain boundary sliding at higher temperature. The mechanism of grain refinement is discussed in detail.     

Behavior of a submicrocrystalline aluminum alloy 1570 under conditions of cyclic loading

A study of the resistance to fatigue-crack growth in a submicrocrystalline alloy Al-6% Mg-0.3% Sc-0.4% Mn in combination with a precision analysis of the fracture surface of the samples has been performed. A comparison of crack resistance between coarse-grained and submicrocrystalline states of this alloy showed that only at the stage of near-threshold crack growth the velocity of fatigue-crack propagation in the submicrocrystalline state proves to be higher than that in the coarse-grained state. At the stage of linear crack growth, the fatigue-crack propagation becomes insensitive to the grain size. Upon transition to the stage of accelerated crack growth, the velocity of crack propagation in the submicrocrystalline alloy is retarded. A fractographic analysis of the fracture surface of the samples indicates that the retardation of the fatigue-crack growth in the submicrocrystalline alloy is connected with a gradual transition from the intercrystalline to the transcrystalline mechanism of fatigue fracture of the material.     

Role of Tungsten in the Tempered Martensite Embrittlement of a Modified 9 Pct Cr Steel

The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M₂₃C₆ carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm^?2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm^?2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M₂₃C₆ carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm^?2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M₂₃C₆ carbides.