Search

In order to investigate the effect of titanium addition on the precipitating behavior of inclusions and corrosion resistance of niobium stabilized ferrite stainless steel, experiments were conducted in a high frequency vacuum induction furnace for smelting titanium and niobium stabilized ferrite stainless steel in argon atmosphere, and the composition, morphologies and size of inclusions in the samples were investigated. Precipitating behavior of the inclusions and intergranular corrosion resistance of the samples were analyzed by CSLM. Corrosion resistance of the steel in 2% NaHSO3 solution was tested by using electrochemistry comprehensive test instrument. The results show that inclusions in the as cast steel mainly are rectangle TiN, TiC, NbC and complex inclusions with TiN or TiC as core packed by NbC, and their size is about 1~5μm. There are a few nearly spherical complex inclusions with Al-Mg-Si-Ti-O as core packed by TiN, TiC, NbC or their complex inclusions. The spherical inclusions become rectangle with the increase of titanium addition, and the quantities of inclusions which size is larger than 5 μm increase. Precipitates increase during heat treated and grain size of the steel becomes a little smaller with the increase of titanium content in the steel. The grain boundary of the steel becomes stabilization and intergranular corrosion resistance enhances with the increase of titanium content in the steel according to the online analysis results. Passivation current density of the steel becomes smaller and passive potential range becomes wider in 2% NaHSO3 solution at 30°C with the increase of titanium content in the steel which indicates corrosion resistance of the steel being enhanced.

Research on ultrasonic extrusion under different process parameters for 45 steel shaft based on orthogonal test is carried out. The influences of various process parameters on shaft surface roughness and micro hardness are analyzed. The experimental results show that the influences of tool radius, pre-pressure, feed rate and rotating speed in the ultrasonic extrusion on surface roughness and micro hardness are different, but there are optimal values in the given experimental conditions. Compared with conventional extrusion, it can reduce the part surface roughness and improve surface micro hardness significantly in the process of ultrasonic extrusion.

Two-dimensional ultrasonic vibration was introduced into common rolled extrusion, effect of the process parameters including tool head radius, feed speed, preload and spindle speed on the 45 steel shaft surface roughness were analyzed through orthogonal experiments. Experimental results show that lower value of surface roughness may be obtained in the process of two-dimensional ultrasonic rolled extrusion than that of common rolled extrusion, and the influence order of process parameters on surface roughness is feed speed, spindle speed, preload and tool head radius; the influence curves of tool head radius and spindle speed on surface roughness are concave curves, and influence curves of feed speed and preload on surface roughness are convex curves, or optimizing process parameters exist. The empirical formula for surface roughness is given using multiple regression analysis based on the experimental results. This study will provide a new technique for finishing precision parts.

Technology of NC-contour evolution ultrasonic assisted creep feed grinding (NC-CEUACFG) blade surface was put forward to solve the difficult problem of machining ceramic blade surface. The static load on the grinding wheel and the influence of the rigidity of the grinding wheel on the surface precision were studied combined with the movement analysis between the blade and grinding wheel in the process of NC-CEUACFG ceramic blade surface, and the physical model of static load may explain the decrease of grinding force and increase of the relative rigidity of the grinding wheel in NC-CEUACFG in theory. The primary experiment of NC-CEUACFG blade surface was carried out according to the experimental results of previous optimized process parameters, and the integral impeller was machined directly in the blank material of Al2O3 ceramic, which indicated the application prospect of such technology.

The gas velocity and particle velocity in and out of the nozzle have great influence on the coating effect in the process of cold spray. An axis-symmetric two-dimensional mathematical model was presented to study the flow field in and out of cold spray nozzle, and the effect of different pressure, temperature, spraying distance and particle diameter on gas axial velocity and particle velocity were researched. The simulation results showed that the gas axial velocity and particle velocity increased when the gas pressure and temperature were increased, spray distance had little effect on the flow field in the nozzle, and small diameter particle was more easily accelerated.

Experiments of ultrasonic polishing the 45# steel shaft without abrasive are carried out by using orthogonal test method to study the polished surface roughness, and experimental results are analyzed with range method. The influence of polishing parameters on the polished surface roughness could be arranged as follows: feed rate, power of generator, preload pressure and radius of the tool head, in which the feed rate brings the most remarkable influence on the polished surface roughness. The surface roughness value reduces at first and then increases when the radius of tool head, preload pressure and power of the generator increase. The surface roughness value increases with the feed rate. Comparative experimental results of ultrasonic polishing without abrasive and the conventional rolling indicate that lower surface roughness value may be obtained by ultrasonic polishing without abrasive.

In order to grind the ceramic blade surface with the Numerical Control contour evolution ultrasonic grinding method using the simple shape grinding wheel, primary comparative experiments of creep feed grinding with and without ultrasonic vibration were carried out to grind Al 2 O 3 ceramics so as to implore the effects of different process parameters on the machined surface quality. It can be concluded that when the direction of ultrasonic vibration is parallel to the direction of creep feed, the value of the surface roughness will be decreased; otherwise the surface quality will become worse. With the ultrasonic grinding method, the slower feed-rate, the smaller grinding depth, the higher grinding speed and the compound feed grinding method should be applied in order to improve the surface quality. The creep feed grinding mechanisms with and without ultrasonic vibration were analyzed theoretically from the experimental results. With the selected grinding parameters resulted from the experiments, the feasibility experiment of ultrasonic grinding ceramic blade surface was carried out.

Ultrasonic machining is a practical process for advanced ceramic machining. Usually, ceramics with complex surfaces are machined with two common ultrasonic assisted contour machining methods, which may be classified as surface/point contact machining mode. While these methods are not suitable to machine some complex surfaces such as blade surface, so an ultrasonic assisted contour machining method using a simple shaped diamond grinding wheel to machine ceramic blade surface is presented, which is named as Numerical Control-Contour Evolution Ultrasonic Assisted Grinding (NC-CEUAG) method. In the NC-CEUAG process, the contour evolution motion of the grinding wheel is controlled by the NC system and the blade surface is the enveloping surface formed by the grinding wheel’ cutting edges when they cut into the ceramic specimen. In this paper, the relative motion between the grinding wheel and the specimen in the process of NC-CEUAG ceramic blade surface is analyzed. The mathematical models of ruled surfaces are constructed. The ceramic blades with ruled surface are machined with selected machining parameters on the retrofitting NC-CEUAG machine tool.