Effect of vanadium and chromium on the microstructural features of V–Cr–Mn–Ni spheroidal carbide cast irons

The objective of this investigation is to study the influence of vanadium（5.0wt%–10.0wt%） and chromium（0–9.0wt%） on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys＇ microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic（based on M7C3）, pearlite, martensite, and austenite. Their combinations and area fraction（AF） ratios are reported to be influenced by the alloys＇ chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic（γ-Fe ＋ М7С3）, preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.

FLOW OF A VISCOUS FLUID PAST A FLEXIBLE MEMBRANE

This paper treats the numerical calculation of a steady two-dimensional viscous flow past a flexible membrane. Both edges of the membrane are fixed in the flow and its chord is set normal to the flow. The numerical calculations of the Navier-Stokes equation based on a finite difference method and a relaxation method are carried out for several values of the membrane tension in cases when the Reynolds numbers are 5, 10 and 20. It is found that the membrane tension has a minimum value below which there is no steady shape of the membrane. Two different shapes of the membrane are possible at a given value of tension: the one is of small deformation, while the other a large deformation. There appear twin vortices in the concave region of the membrane shape if its deformation increases to a certain extent.

Optimization of Cu content for the development of high-performance T5-treated thixo-cast Al-7Si-0.5Mg-Cu(wt.%)alloy

Cu content has been successfully optimized in a thixo-cast and directly aged(T5-treatment)Al-7 Si-0.5 Mg(wt.%)alloy.Even after the 0.5%Cu addition,plate-like Al_(2)Cu(θ’)phases,which contribute to high strengths and large plasticity,are precipitated.The formation of a large fraction of Cu-containing brittle phases could be suppressed as well.Then,the Al-7Si-0.5Mg-0.5Cu alloy exhibits high ultimate tensile strength,0.2%proof stress,and elongation to failure of 296 MPa,209 MPa,and 8.8%,respectively.This results in a high quality index similar to that of solution-treated and subsequently aged(T6-treated)Al-7 Si-Mg alloys.A Cu addition over 1.0%further improves the strengths;however,this leads to poor ductility because of the high fraction of Cu-containing brittle phases.

Present Status of NIRS ECR Ion Sources

Four ECR ion sources have been operated in National Institute of Radiological Sciences(NIRS). Two ECR ion sources supply various ion species for the Heavy Ion Medical Accelerator in Chiba(HIMAC). The 10GHz NIRS-ECR ion source mainly produces C^(2+) ions for the heavy-ion therapy.Ions of Si,Ar,Fe,Kr and Xe are usually produced by the 18GHz NIRS-HEC ion source for physical and biological experiments.The other two compact ECR ion sources with all permanent magnet configuration have been developed for the new generation carbon therapy facility.One of these,the Kei-source,is a prototype which has been installed to the NIRS-930 cyclotron for axial injection.The other source,Kei2-source,is a demonstration source and utilized for the new generation Linac.In addition,both Kei sources have been used to study fundamental properties. In this paper,present status of the ion sources and recent developments are reported.

High-Accuracy Polishing Technique Using Dwell Time Adjustment

Two algorithms for dwell time adjustment are evaluated under the same polishing conditions that involve tool and work distributions.Both methods are based on Preston’s hypothesis.The first method is a convolution algorithm based on the Fast Fourier Transform.The second is an iterative method based on a constraint problem,extended from a one-dimensional formulation to address a two-dimensional problem.Both methods are investigated for their computational cost,accuracy,and polishing shapes.The convolution method has high accuracy and high speed.The constraint problem on the other hand is slow even when it requires larger memory and thus is more costly.However,unlike the other case a negative region in the polishing shape is not predicted here.Furthermore,new techniques are devised by combining the two methods.