GB1582495A - Alloys for machine components subject to mechanical vibration - Google Patents

Description

(54) ALLOYS FOR MACHINE COMPONENTS SUBJECT TO MECHANICAL VIBRATION (71) We, CENTRE DE RECHERCHES METALLURGIQUES-CENTRUM VOOR RESEARCH IN DE METALLURGIE, a Belgian Body Corporate, of 47, Rue Montoyer, Brussels, Belgium, and CENTRE D'ETUDE DE L'ENERGIE NUCLEAIRE C.E.N/ S.C.K., of 200, Boeretang, 2400 Mol, Belgium, A Belgian Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described, in and by the following statement: The present invention relates to alloys suitable for the manufacture of machine components subject to mechanical-vibration, especially those components which are subject to mechanical vibrations at high temperature, such as gas turbine blades and other rotary components.

It is known that, for the above-mentioned purposes, use must be made of alloys having internal damping properties, great strength, and good ductility at temperatures which may reach 700"C or even higher sometimes. In particular this is the case when it is desired to ensure a sufficiently long life for the first rows of blades in turbines, which are subjected to particularly severe mechanical vibrations at high temperature.

In numerous applications, especially those in which materials are subjected to mechanical vibrations, the damping capacity of a material may be more important than other properties such as the fatigue limit. The damping capacity of a material is actually due to four factors, i.e. plastic deformation, the thermo-elastic effect, the magneto-elastic effect, and atomic diffusion. The magneto-electric effect is surely the most important in the case of alloys designed to be used in industry. It is well recognized that ferromagnetic alloys have, for a number of purposes, better properties than non-magnetic alloys. It has been found that the high damping capacity of ferromagnetic alloys is due to a magneto-mechanical hysteresis effect. The energy dissipated during a tensile stress deformation cycle because of the magneto-mechanical effect is responsible for the damping capacity of the material.

A material having a high damping capacity is thus a magnetic material having as high as possible a Curie temperature, while a compromise must be found between the various properties required, i.e. strength at working temperature, damping capacity, oxidation resistance, and ductility at ambient temperature.

In view of the above considerations, a number of industrial materials such as, on the one hand, steels of the AISI 403 type (12% Cr) and the AISI 422 type (12% Cr Mo W V) type and. on the other hand, cobalt-nickel alloys termed NiVCo, and the 70% Mn 30% Cu alloy, have become generally adopted, especially in the manufacture of turbine blades. The choice of alloying elements capable of hardening the ferromagnetic matrices is practically limited, because the various additions have in general the effect of lowering the Curie point .of an alloy and thus the damping capacity of the material.

For one reason or another, these alloys have disadvantages which limit the possibility of using them in the above-mentioned applications. Among these disadvantages one should mention insufficient resistance to creep at high temperature, manufacturing difficulties in assembly due to hardness or to fragility or to indeformability, decrease in damping capacity under high dynamic and static stresses, and high cost.

The present invention concerns an alloy particularly suitable for the above-mentioned applications, and in general for machine components which are subject, in use, to more or less severe vibrations due to high speed of rotation, to alternating movements, or to speed variations.

This alloy is characterized by a composition, by weight, meeting the following relationships: 5% a Cr S 25% 0.05% Ti S 5% 0 < Mo S 5% the balance being Fe and its usual impurities.

It has been found that the above material simultaneously exhibits good properties of high-temperature strength, ductility, creep resistance, and internal damping, up to temperatures of the order of 700"C.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a graph of internal damping versus dynamic strain, at 0.5 Hz, for a component made of a conventional alloy, at various static stresses; Figure 2 is a graph similar to Figure 1, for a component according to the invention, at various static stresses; Figure 3 is a graph of internal damping, at 0.5 Hz, versus ageing temperature, for a component according to the invention subjected to different heat treatments; Figure 4 is a graph similar to Figure 2, for a component according to the invention, at various static stresses; and Figure 5 is a graph similar to Figure 1, for components made of various alloys.

The various compositions of the alloys referred to below and in the graphs are given in the following Table, together with the thermo-mechanical treatment (if any given to alloy.

TABLE Alloy Fe Cr Ni Mo Ti TiO2 % % % % % % AISI 410 balance 13 -- -- -- - AISI 316 " 16 13 1 -- - B 3 E " 13 -- 1.5 2.5 - 816W* " 13 -- 1.5 3.5 0.5 817 13 -- 1.5 3.5 1.0 818* " 13 -- 1.5 3.5 1.5 819* t3 -- 1.5 3.5 2.0 B extrusion at 1 1000C * extrusion at 11000C, reduction at 1050-1100 C from 19 to 10 mm reduction at 25"C from 10 to 8.6 mm heat treatment: 1 hour under argon at 1050"C By way of comparison, Figures 1 and 2 show, at 0.5Hz, the internal damping (in terms of the logarithmic decrement 6) as a function of the dynamic strain Y at various static stresses at room temperature. Figure 1 relates to the conventional AISI 410 steel whose composition is set forth in the above Table, while Figure 2 relates to an alloy designated B3E whose composition is also given in the Table.

By heat treating the alloy in question. it is possible to modify the shape of the damping versus strain curve by either varying the maximum damping value of the corresponding tension. By ageing and solution heat treatment it is possible to adjust the damping capacity of the alloy, as illustrated in Figure 3 after various thermo-mechanical treatment.

Hardening of the metal matrix, no longer based on the formation of carbides but on precipitation of a X (chi) phase of the Fel7 Cr,7 (Ti, Mo)5 type, facilitates the use of the alloy at a temperature of 700"C owing to the stability of the precipitated phase. In Figure 3, internal damping at 0.5 Hz at a static stress T of 20 MNm at room temperature is plotted against ageing temperature for the alloy B3E extruded at 11000C and then soaked for various times at the ageing temperature.

Furthermore, Figure 4 illustrates the internal damping capacity at 0.5 Hz as a function of the dynamic strain at various levels of the static loads (MNm-2) applied, for the alloy designated 817 in the above Table, which is a dispersion-strengthened ferritic steel. This graph shows particularly high damping values under large dynamic stresses, and small damping sensitivity with respect to the static load applied, which constitutes a further advantage.

Figure 5 shows how the values of the internal damping vary as a function of the composition of the alloy, at a single level (high level) of static load (o) of 220 Mum~2. This graph also indicates the damping curve corresponding to the conventional austenitic alloy AISI 316. One can note the large difference between this curve and the curves corresponding to the other alloys, among which that indicated by 818 is particularly interesting.

According to a variant of the invention and as illustrated in Figures 4 and 5, it has been found that it is possible to improve the properties of the alloy by incorporation of a finely dispersed inert phase in the matrix and by taking advantage of the possibilities of powder metallurgy. According to a preferred composition, the addition of one or more of the following oxides to the metal matrix, in the indicated proportions, was found to be particularly satisfactory: TiO2 S 4% by volume Y203 S 4% by volume MgO S 4% by volume Al203 S 4% by volume.

WHAT WE CLAIM IS: 1. A machine component which, in use, is subject to mechanical vibration, the component being made of an alloy containing: 5 to 25 wt.% Cr, 0.05 to 5 wt. % Ti, and zero to 5 wt.% Mo, the balance being Fe and impurities.

2. A machine component which in use, is subject to mechanical vibration, the component being made of an alloy containing : 5 to 25 wt.% Cr; 0.05 to 5 wt.% Ti; zero to 5 wt.%Mo; and at least one oxide selected from the group consisting of maximum 4 vol.% TiO2, maximum 4 vol.% Y203, maximum 4 vol.% MgO, and maximum 4 vol.% Awl203; the balance being Fe and impurities.

3. A component as claimed in claim 1 or 2, which, in use, is subject to rotational movement causing mechanical vibration.

4. A component as claimed in claim 3, being a turbine blade.

5. A machine component as claimed in claim 1 or 2, substantially as described herein with reference to Figures 2 to 5 of the accompanying drawings.

6. A machine including a component according to any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. at a temperature of 700"C owing to the stability of the precipitated phase. In Figure 3, internal damping at 0.5 Hz at a static stress T of 20 MNm at room temperature is plotted against ageing temperature for the alloy B3E extruded at 11000C and then soaked for various times at the ageing temperature. Furthermore, Figure 4 illustrates the internal damping capacity at 0.5 Hz as a function of the dynamic strain at various levels of the static loads (MNm-2) applied, for the alloy designated 817 in the above Table, which is a dispersion-strengthened ferritic steel. This graph shows particularly high damping values under large dynamic stresses, and small damping sensitivity with respect to the static load applied, which constitutes a further advantage. Figure 5 shows how the values of the internal damping vary as a function of the composition of the alloy, at a single level (high level) of static load (o) of 220 Mum~2. This graph also indicates the damping curve corresponding to the conventional austenitic alloy AISI 316. One can note the large difference between this curve and the curves corresponding to the other alloys, among which that indicated by 818 is particularly interesting. According to a variant of the invention and as illustrated in Figures 4 and 5, it has been found that it is possible to improve the properties of the alloy by incorporation of a finely dispersed inert phase in the matrix and by taking advantage of the possibilities of powder metallurgy. According to a preferred composition, the addition of one or more of the following oxides to the metal matrix, in the indicated proportions, was found to be particularly satisfactory: TiO2 S 4% by volume Y203 S 4% by volume MgO S 4% by volume Al203 S 4% by volume. WHAT WE CLAIM IS:

1. A machine component which, in use, is subject to mechanical vibration, the component being made of an alloy containing: 5 to 25 wt.% Cr, 0.05 to 5 wt. % Ti, and zero to 5 wt.% Mo, the balance being Fe and impurities.

2. A machine component which in use, is subject to mechanical vibration, the component being made of an alloy containing : 5 to 25 wt.% Cr; 0.05 to 5 wt.% Ti; zero to 5 wt.%Mo; and at least one oxide selected from the group consisting of maximum 4 vol.% TiO2, maximum 4 vol.% Y203, maximum 4 vol.% MgO, and maximum 4 vol.% Awl203; the balance being Fe and impurities.

3. A component as claimed in claim 1 or 2, which, in use, is subject to rotational movement causing mechanical vibration.

4. A component as claimed in claim 3, being a turbine blade.

5. A machine component as claimed in claim 1 or 2, substantially as described herein with reference to Figures 2 to 5 of the accompanying drawings.

6. A machine including a component according to any preceding claim.