CS252709B1 - Method of testing-bar making for refractory alloys-made products' mechanical properties testing - Google Patents

Abstract

The solution relates to the method of making the test rods for mechanical properties testing of nickel alloys or cobalt with a small cross-section or hollow thin-walled products, cast from the test material base product such as mono- or bicrystalline model to shell ceramic without using a core. The subject of the solution is that on mono- or a bicrystalline hollow tube molding with surface to cross section x = 44.33 to 31.35 is cleared from two opposite hillsides surface over the rest of the area removed by grinding with radii R = 3 millimeter part of the base material as and the ceramic part inside the tube depths 23 to 25% of total cross-section with retention two longitudinal opposite ones parts of walls of 25 to 30 ° / overall of the test rod and after removal the remaining ceramics in the interior the parts are removed on the active parts by the sharp edges edges.

Description

The invention relates to a method of making a test bar for testing the mechanical properties of low cross-section refractory nickel or cobalt alloys or hollow thin-walled articles cast from a base material of a test article by a melt-ceramic shell mold without a mono- or bicrystalline core.

The strength characteristics of cast or hollow blade materials such as creep resistance, fatigue resistance, tensile strength, ductility, and other properties are currently found on solid bars made of cylindrical or conical shaped castings.

Problems of testing the strength characteristics are particularly evident in the materials used for the production of gas turbine blades, namely refractory nickel or cobalt alloys, which are characterized by very poor machinability.

Solid bars made of cylindrical or conical castings generally do not have properties close to those of blades with a small cross-section or hollow with a very small cross-section. This is because they crystallized in a different way than thick-walled castings.

The hollow vanes are also characterized by a substantially higher surface to cross-sectional value than a solid bar, further deteriorating model similarity. Cracks arising from the mechanical stress of materials emanate largely from the surface, with the exception of the existence of major internal failures, i. j. supercritical size and therefore solid bars provide higher values of measured properties.

In view of the difficult machinability of nickel or cobalt refractory alloys, an attempt is made to produce test bars with clamping heads in a precision casting manner in order to minimize their production costs. This method has its limitations. There is a risk of hot cracking in the measured length of the test rods due to limited shrinkage during the cooling process and from the casting temperature in a very rigid and solid shell ceramic form.

These drawbacks are eliminated and technical progress is solved by the method of making a test rod according to the invention, which consists in that on a tube cast from the base material of the test product by a meltable model into a shell ceramic mold without using a core as mono- or bicrystal. ends and by threading these, remove two parts of the test rod material as well as the part of the ceramic inside the pipe to a depth of 23 to 25% of the total cross-section from the two opposite sides of the remaining part of the surface by grinding with radii R - 3 mm tubes with a width of 25 to 30% of the total cross-section of the test rod and where, after removal of the remaining ceramic in the inner part, edge burrs are removed on the active parts of the test rod. The ratio of the surface of the hollow tube to the cross-section x - = 44.33 to 31.35.

The production of the preform for making the test rod with or without precision casting, either by controlled crystallization or without, so that a series of rods of 20 pieces can be made in one cycle.

In terms of model similarity, the test rod made according to the invention provides real values of the measured parameters related to the properties of hollow or solid blades with a very small cross-section, which makes it possible to more reliably estimate the life of the products. In the process of cooling the hollow tube-shaped blank intended for the manufacture of the hollow test rod, there can be no significant braking on the shrinkage of the casting in the shell ceramic form, and the manufacturing rod does not contain hot cracks, which are essential features of higher effect. Another advantage is the simple defectoscopic inspection of the inner surface of the test specimen, which significantly affects the reliability in determining the properties of hollow blade materials.

In addition to reliability in terms of model similarity, such a shape of the casting body has a number of advantages in terms of its production. The problem of core production with high demand for its utility value, as well as the problem of molding the core into the wax model and removing this from casting by difficult leaching, etc., will be eliminated. It is possible to produce casting walls of the required depth as a simulation of the cross-sectional depth of the model blade. The equivalent wall thickness of the hollow blade or blade full of the blade can be tested.

In the attached drawing, FIG. 1, a test rod is shown in elevation in two views, with an equivalent cross-section equal to that of a solid rod of 4 mm diameter.

Fig. 2 shows in cross-section the converted model and dimensional adjustments in the test rod manufacturing process.

Example

The method and constructional modifications of the invention have made a test rod, by precision casting using a fusible model, of a refractory nickel alloy intended for the manufacture of turbine blades. Tube wall thickness 2 mm, diameter 12 mm, length 60 mm. No ceramic core was used for casting. After removing the ceramic on the outer surface of the pipe, a M12 thread was cut at both ends at a length of 15 mm. By grinding, a portion of the material "A" was removed from the tube and a portion "B" from the ceramic inside the tube, as shown in FIG.

2. Both parts of the material and the ceramics were ground to a length of 30 mm with radii R = 3 mm and to a depth of 2.86 mm according to previous calculations and from experience on test specimens. Remaining ceramics inside the rod was removed, which was severely disturbed by grinding, so it was sufficient to remove it with a hammer. Finally, the rod was cleaned of edge burrs and used directly without further surface treatment to test the mechanical properties of products made of the same material. Test conditions: At 900 ° C and an external load of 300 MPa creep test, the time to failure was monitored. The time to failure values obtained on the single crystal bar of FIG. 1 were in the range of 3 to 5 times higher than on bars with a polycrystalline structure of known shapes. The model match was related to the same cross-sectional size of the bars with the circular cross-section and the cross-section of FIG. First

Ductility values were achieved 3 to 4 times higher than that of a rod with a polycrystalline structure of conventional use.

Claims (2)

SUBJECT Method of making a test rod for testing the mechanical properties of nickel or cobalt refractory nickel or cobalt alloys or hollow thin-walled products cast from the base material of the test article by melting the core into a shell-free ceramic mold, forming heads of the test rod at both ends thereof are threaded, characterized in that on a mono- or bicrystalline hollow-tube casting with a surface to cross-section ratio x = 44.33 to 31.35, the two opposite sides of the surface to be cleaned are removed by grinding with radii R = 3 mm part of the base material as well as the ceramic part inside the pipe to a depth of 23 to 25% of the total cross-section, leaving two longitudinally opposite sides of the wall with a width of 25 to 30% of the total cross-section. the edges in the active part are removed on the active part.