Plasma Nitriding Behavior of Fe-C-M (M = Al, Cr, Mn, Si) Ternary Martensitic Steels

Change in surface hardness and nitrides precipitated in Fe-0.6C binary and Fe-0.6 mass pct C-1 mass pct M (M = Al, Cr, Mn, Si) ternary martensitic alloys during plasma nitriding were investigated. Surface hardness was hardly increased in the Fe-0.6C binary alloy and slightly increased in Fe-0.6C-1Mn and Fe-0.6C-1Si alloys. On the other hand, it was largely increased in Fe-0.6C-1Al and Fe-0.6C-1Cr alloys. In all the Fe-0.6C-1M alloys except for the Si-added alloy, fine platelet alloy nitrides precipitated inside martensite laths. In the Fe-0.6C-1Si alloy, Si-enriched film was observed mainly at a grain boundary and an interface between cementite and matrix. Crystal structure of nitrides observed in the martensitic alloys was similar to those in Fe-M binary ferritic alloys reported previously. However, there was a difference in hardening behavior between ferrite and martensite due to a high density of dislocations acting as a nucleation site of the nitrides and partitioning of an alloying element between martensite and cementite changing the driving force of precipitation of the nitrides.     

New digital control and protection equipment using multiprocessor architecture of distributed functions for power system

Control and protection of equipment in power systems generally require a high-information processing capability to cope with today's power system requirements. Then, new digital control and protection equipment have been developed using high-speed and high-precision processors. Essential requirements for the new control and protection equipment are a multiprocessor architecture of distributed functions to retain sufficient computing power (fast and high-precision operations), and flexible and expandable hardware with high reliability. In multiprocessor architecture, it is important to determine how the distributed processors share the functions. By analysis and synthesis of relaying and control processings, we divided them into six processing circuits. This paper proposes a multiprocessor architecture of distributed functions, using 32-bit floating-point and 16-bit microprocessors depending on the computational requirements. In addition a digital filter for fast sampled data is described along with performance of a digital relay.     

Numerical simulation of lateral phase distribution in turbulent upward bubbly two-phase flows

New constitutive models for the interfacial forces acting on bubbles were developed for accurately predicting the lateral phase distribution in turbulent bubbly two-phase flow in vertical channels. Several experimental measurements have revealed that the lateral void profile in bubbly two-phase flow varies from the void peaking near the wall to the almost flat distributions as the liquid velocity increases. However, within the authors' knowledge, the effect of liquid velocity on the void profile has not been successfully predicted by the existing models; this would indicate the strong limitation of the existing multidimensional two-phase flow models. In view of these, the validity of the present constitutive models was tested in varied conditions of the liquid velocity as well as the bubble size. Since several assumptions were required in the models mainly due to the insufficient knowledge of the bubble motion, further improvements should still be needed. Nevertheless, the predicted lateral phase distributions were found to be in reasonably good agreement with available experimental data. It is hence expected that the present constitutive models can effectively be used in the practical applications and also be the base of the more sophisticated ones.     

Convective heat transfer of gaseous solid suspension flow in a curved tube

Experimental study was performed on the convective heat transfer of gaseous solid suspension flow within helically coiled circular tube. The results show that the increase in heat transfer is greater than that due to the simple contribution of the increased heat capacity as the flowing media. This suggests that the addition of the suspended phase into the flows with curved stream lines can bring about the substantial reduction in the convective heat transfer resistance in the vicinity of the channel walls of the outer curvature portion. However, slight decrease in mixture Stanton number is also observed at the slight loading ratio region and the sublayer disturbing effect is seen to be gradually saturated at the higher loading region. Accordingly, overall reduction in the turbulence level also exists in the turbulent core of the flow and it is expected that there is an optimum solid loading ratio at which the viscous sublayer disturbing effect on the overall heat transfer performance is most effective.     

A method for measuring transients caused by interrupting currentusing a transmission line terminated in its characteristics impedance

A measurement method of transients caused by interrupting a current is described. In consideration of the fast transients and high-frequency discharge phenomena due to interrupting the current, a transmission-line system was introduced. It consists of a coaxial switch, coaxial cables as transmission lines on the right and left sides of the switch, and termination resistors. When the current is interrupted by the switch, the waveform across the termination resistor is measured by an oscilloscope. The impedance-matching technique for the cables was employed to minimize the effects of reflected waves. That is, the resistors were designed to match the characteristic impedance of the cables. The characteristics of the system were measured by a network analyzer. The VSWR of the system was within 1.33 in the frequency range below 500 MHz. The time-domain measurement using a transmission-line system terminated in its characteristic impedance clears up the process of the complicated transients caused by interrupting current     

Automotive Application of Advanced Superalloys

Based on the testing reported here, a new Ni-based superalloy has been adopted for use in Mazda RX-7 heat-resistant turbochargers. The new alloy exhibits a high temperature stability of the γ phase, resisting the initial stage of creep rupture. Casting parameters and chemistries are varied to produce a directionally solidified columnar structure, which eliminates internal grain boundary rupture sites. The Mazda super-high temperature turbocharger was used to achieve a world speed record (GT-C class) of 238.442 mph at Bonneville, Utah, last August.