Wenbin SHENG
,
Dong LI
,
Rui YANG
,
Yuyin LIU
,
Jingjie GUO
,
Jun JIA
材料科学技术（英文）
Ti-48Al-2Cr-2Nb automobile exhaust valves were formed with permanent mold centrifugal cast method and their surface layer structure, microstructure, elements distribution and mechanical properties were analyzed by SEM, XRD and EMPA etc. Furthermore, the HIPped valves were tested on 483Q diesel engine. Results showed that the element distribution of TiAl based alloy exhaust valves was uniform and their microstructure was refined. The typical mechanical properties of HiPped exhaust valves were sigma (b)=670 MPa, sigma (0.2)=527.5 MPa and delta =3%. Engine test showed that the valves had excellent airtightness and wear resistance properties and satisfied the requirements of engine successfully.
关键词:
Acta Physica Sinica
A mathematic model of mold filling and solidification in horizontal centrifugal casting is built up. Based on this model, the temperature field and the flow field in horizontal centrifugal casting are numerically simulated. The hydraulic experimental results are compared with numerical simulations, indicating that the mathematic model is accurate. Experimental results show that liquid fills the mold in the manner of a spiral trajectory in the centrifugal casting process. The filling pattern tends to be more uniform with the increase of rotational speed. The present study has a guiding significance to the production of horizontal centrifugal casting roll.
关键词:
horizontal centrifugal casting;mathematic model;numerical simulation;hydraulic experiment;microstructure evolution
Intermetallics
The mould filling process and solidification of TiAl exhaust valves by centrifugal investment casting have been simulated. Two types of runner and gating systems are designed and analysed. In the preliminary design, a "tree-type" set up system is used and a significant amount of porosity is found in many valves of the simulation result. The fluid field simulations indicate that moulds are not filled well in the preliminary design, leading to the last hot spots deviating from the center line of castings. Casting defects deviated from the center line of the part, and the degree of deviation is affected by the mould filling process and temperature fields. Simulation results reveal that castings do not experience sequential solidification, so the design is not proper for the exhaust valve. Comparing the experimental and simulation results, the range of Niyama criterion in the centrifugal TiAl casting is defined, which is 0.14-0.20. Several key factors such as pouring temperature, mould temperature and rotation speed are studied in detail. An optimized design is developed in which valves are rearranged to reduce the neighboring heat radiation effect, and the gate size is enlarged to keep the feeding path open. Sound exhaust valves have been produced successfully using the optimized technique. (C) 2007 Elsevier Ltd. All rights reserved.
关键词:
titanium aluminides;based on TiAl;casting;near-net-shape;manufacturing;automotive uses;gamma;aluminides;alloys;parts
GE Yunlong YANG Yuansheng JIAO Yuning HU Zhuangqi Institute of Metal Research
,
Academia Sinica
,
Shenyang
,
ChinaGAO Yunyan JIA Guanglin Northeast University of Technology
,
Shenyang
,
China associate professor
,
Institute of Low Energy Nuclear Physics
,
Beijing Normal University
,
Beijing
,
100875
,
China
金属学报(英文版)
A new technique of centrifugal casting under electromagnetic field was firstly proposed and investigated.Taking a heat resisting alloy steel 25Cr20Ni and an Al-Cu alloy as examples,products,though their length,diameter and wall thickness are varied,re- vealed so superior macrostructures that the mechanical properties are much improved in comparison with conventional centrifugal casting.
关键词:
electromagnetic field
,
null
,
null
,
null
Intermetallics
Centrifugal casting has been used to cast TiAl car valves. The casting has been carried out in vacuum using induction melting furnace coupled to a CaO crucible, which offers a maximum superheat of approximately 180 degrees C and much improved filling over normal cold wall induction furnace. In this work, the effects of the casting conditions, including superheat, rotation speed at one mould temperature have been investigated in terms of the product integrity and porosity and the microstructure of the valves. The mechanical properties and oxygen contents of cast stems with various degrees of superheat have been measured at room temperature. The as-cast car valves and some HIPped car valves have been successfully engine-tested. The feasibility for mass production of TiAl car valves and realistic costing for producing car valves using centrifugal casting and CaO crucible are currently also being assessed. (c) 2004 Elsevier Ltd. All rights reserved.
关键词:
titanium aluminides;based on TiAl;mechanical properties at ambient;temperature;casting;microstructure;automotive uses;including engines;tensile properties;microstructure;alloy
MA Zongyi YAO Zhongkai Harbin Institute of Technology
,
Harbin
,
China
金属学报(英文版)
The SiC_w/Al composite prepared by squeeze casting has a combination of superior room temperature specific strength and modulus together with excellent thermal properties.The extrusion can make an improvement on the strength and ductility of the composite from 582 MPa as squeeze casted up to 639 MPa,and on the transformation from isotropic to the anisotropic structure.This seems to be explained by the orientation of whiskers and the densification of dislocations in matrix.TEM observation indicates that the stacking fault is the usual planar defect on the SiC_w surface. composite;;SiC whisker;;Al alloy;;microstructure
关键词:
composite
,
null
,
null
,
null
Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science
A theoretical analysis is presented to obtain gradient distribution of particles in centrifugal field, by which the particle distribution in gradient composite can be predicted. Particle movement in liquid is described and gradient distribution of particles in composite is calculated in a centrifugal field during the solidification. The factors which affect the particle distribution and its gradient are discussed in detail. The theoretical analysis indicates that a composite zone and a blank zone exist in gradient composite, which can be controlled to the outside or inside of the tubular composite by the density difference of particle and liquid metal. The comparison of the SiC particle distribution in Al matrix composite produced by centrifugal casting between the theory model and the experiment denotes that the theoretical analysis is reasonable.
关键词:
metal-matrix composites
