The existence of defects in TC4 titanium forgings will affect the processing quality or processing quality of the subsequent processes, and some will seriously affect the performance and use of titanium forgings and titanium alloy forgings, and even greatly reduce the service life of the finished products and endanger safety . Therefore, in order to ensure or improve the quality of titanium forgings, in addition to strengthening quality control in the process and adopting corresponding measures to prevent the occurrence of defects in titanium forgings, necessary quality inspections should also be carried out to prevent subsequent processes (such as heat treatment, surface treatment, Titanium forgings with defects that have adverse effects on cold processing and service performance flow into the subsequent process. After the quality inspection, remedial measures can be taken for the manufactured titanium forgings according to the nature of the defect and the degree of influence to use, so that it meets the technical standards or requirements for use.
Therefore, the quality inspection of titanium forgings in a sense, on the one hand, is to check the quality of the manufactured titanium forgings, on the other hand, it is to point out the improvement direction for the forging process, so as to ensure that the quality of the titanium forgings meets the requirements of the technical standards for titanium forgings. And meet the requirements of design, processing and use. The quality inspection of titanium forgings includes the inspection of appearance quality and internal quality. Appearance quality inspection mainly refers to the inspection of the geometric size, shape, surface condition and other items of titanium forgings; internal quality inspection mainly refers to the inspection of chemical composition, macrostructure, microstructure and mechanical properties of titanium forgings.
Specifically, the appearance quality inspection of titanium forgings is to check whether the shape and geometric dimensions of the titanium forgings meet the specifications of the drawings, whether the surface of the titanium forgings are defective, what are the defects, and what are their morphological characteristics. The inspection content of the surface condition is generally to check whether the surface of the titanium forgings has surface cracks, folds, wrinkles, pits, orange peel, blisters, scars, corrosion pits, bruises, foreign objects, underfill, pits, lack of meat, Defects such as scratches. The internal quality inspection is to check the internal quality of the titanium forging itself. It is a quality condition that cannot be found by the appearance quality inspection. It includes the inspection of the internal defects of the titanium forgings and the inspection of the mechanical properties of the titanium forgings. For important and key parts Or large titanium forgings should also be subjected to chemical composition analysis. For internal defects, we will inspect the titanium forgings through low-power inspection, fracture inspection, and high-power inspection to check whether there are internal cracks, shrinkage holes, porosity, coarse crystals, white spots, dendritic crystals, and streamlines that do not conform to the shape and streamlines. Defects such as turbulence, flow through, coarse crystal ring, oxide film, delamination, overheating, overburning organization, etc. For the mechanical properties, it is mainly to check the normal temperature tensile strength, plasticity, toughness, hardness, fatigue strength, high temperature instantaneous rupture strength, high temperature permanent strength, permanent plasticity and high temperature creep strength.
After the titanium forgings are made into parts, their stress, importance, and working conditions are different during use, and the materials and metallurgical processes used are also different. Therefore, different parts of the titanium forgings are divided according to the above conditions and according to the requirements of this department. According to different categories, different departments and different standards have different classifications of titanium forgings. But no matter what, the overall quality inspection of titanium forgings is inseparable from two major types of inspections, namely, the inspection of appearance quality and internal quality, but the types of titanium forgings are different, and the specific inspection items, inspection quantities and inspection requirements It's different. For example, some industrial departments classify structural steel, stainless steel, and heat-resistant steel titanium forgings into category IV for inspection, and some departments classify aluminum alloy titanium forgings and die titanium forgings into category III according to their usage conditions, and some There is serious grinding wheel adhesion during the grinding process of aluminum-titanium rod, and the grinding force and grinding temperature are very high, so grinding burns and cracks simply occur. When grinding titanium rods with ordinary abrasives, even if the grinding depth is small, grinding burns and cracks will occur on the ground surface. Approximately yellow-brown spots, hairline-like cracks, the direction of which is straight with the grinding direction, with a large amount of grinding, there will be scale-like wrinkles and plastic deformation metal deposits on the surface. What kind of substance is this? Let's take a look at the chemical reaction formula of silicon carbide abrasive grain grinding titanium rod: SiC+Ti→TiC+Si. , And look at the oxidation reaction formula of silicon carbide abrasive grains at a certain atmospheric temperature: SiC+2O2→SiO2+CO2.
Titanium rods have been widely used in the aerospace industry at home and abroad for their outstanding heat and corrosion resistance and particularly high specific strength. To align the grinding burn problem that occurs easily in the grinding process of titanium rods, choose the leading test method to measure the grinding force, grinding temperature, workpiece surface roughness and surface trace, and surface layer metallography during the grinding process. The arrangement and microhardness change rules were analyzed and discussed. The research results show that the TC6 titanium rod burns when the grinding temperature exceeds 600℃. Surface tracing gradually deteriorates with the increase of grinding temperature. When severe burns occur, cracks occur on the surface of the workpiece, and the direction is roughly straight with the grinding direction. When the workpiece is burned, the metallographic arrangement of the surface layer of the material changes, and the α-phase particles are significantly larger, which reduces the physical and mechanical properties of the titanium rod. The research results provide theoretical and experimental basis for seeking optimized high-efficiency and high-precision titanium rod grinding processing technology.
In the meantime, a part of the carbon atoms will be scattered to the surface of the workpiece to be ground. Under the effect of the sliding shear force, the SiO2 oxide film will be peeled off, forming SiC abrasive particles oxidized wear, while the surface of the workpiece will leave a loose layer of oxygen and carbon elements, which is counterproductive Loss of the carbon weakening layer occurs on the surface of the abrasive particles, the hardness of the SiC abrasive particles decreases, the grinding force increases, the wear of the grinding wheel increases, and the increase in the grinding temperature is inevitable. From the microscopic level, the process of the formation of abrasive particles and adhesion is that the cutting edge first appears small area adhesion and gradually large area adhesion, the abrasive particles are finely broken, and then the abrasive particles are broken and fall, plastic deformation occurs in the grinding area of the titanium rod. The abrasive grains and the workpiece are bonded to each other, which has both physical adsorption and chemical adsorption effects. With the relative sliding shear force, the processed material is transferred to the abrasive grains. This is the entire process of the grinding wheel adhesion.
The adhesion of the grinding wheel simply constitutes a blockage, which increases the temperature of the grinding area, and the grinding surface produces distributed grinding burns along the workpiece layer, accompanied by a degeneration layer and residual stress. In the grinding cooling process, when the grinding depth is large, the density of the oxide film on the grinding surface reaches the critical temperature, and the temperature of the grinding arc area will rise sharply due to the film formation of the grinding fluid. The cooling effect Getting worse. When the elevated temperature exceeds the limit that the usual abrasive can withstand, the abrasive grains will fall due to softening damage. Therefore, it is necessary to choose a new super hard grinding wheel to further increase the high temperature tolerance of the grinding arc zone. Alloy and copper alloy titanium forgings are classified into Category IV for inspection.