Density-optimized molybdenum alloy

Abstract

The present invention relates to a density-optimized and high temperature-resistant alloy based on molybdenum-sili-con-boron, wherein vanadium is added to the base alloy in order to reduce the density.

Claims

1. A molybdenum alloy with 5 to 25 at % silicon, 0.5 to 25 at % boron, and 20 to 40 at % vanadium as well as the remainder of molybdenum, wherein the proportion of molybdenum is at least 40 at %, wherein the molybdenum alloy has a molybdenum-vanadium mixed crystal matrix and at least one silicide phase distributed therein, and the density of the molybdenum alloy is less than 8 g/cm.sup.3, and wherein at least one silicide phase is selected from (Mo,V).sub.3Si, (Mo,V).sub.5SiB.sub.2, and (Mo,V).sub.5Si.sub.3.

2. The molybdenum alloy according to claim 1, additionally containing titanium (Ti) in an amount of 0.5 to 30 at %.

3. The molybdenum alloy according to claim 2, wherein the content of Ti is 0.5 to 10 at %.

4. The molybdenum alloy according to claim 1, additionally containing one alloy element or a plurality of alloy elements selected from the group composed of Al, Fe, Zr, Mg, Li, Cr, Mn, Co, Ni, Cu, Zn, Ge, Ga, Y, Nb, Cd, Ca, and La, each in a content of 0.01 at % to 15 at %, and/or one alloy element or a plurality of alloy elements selected from the group composed of Hf, Pb, Bi, Ru, Rh, Pd, Ag, Au, Ta, W, Re, Os, Ir, and Pt, each in a content of 0.01 at % to 5 at %.

5. The molybdenum alloy according to claim 1, wherein the proportion of silicide phases is at least 30 at %.

6. The molybdenum alloy according to claim 1, wherein the alloy has a structure with a Mo—V mixed crystal matrix and (Mo, V).sub.3Si and/or (Mo,V).sub.5SiB.sub.2 distributed therein.

7. The molybdenum alloy according to claim 6, wherein the phase (Mo,V).sub.5Si.sub.3 is additionally present.

8. The molybdenum alloy according to claim 2, additionally containing one alloy element or a plurality of alloy elements selected from the group composed of Al, Fe, Zr, Mg, Li, Cr, Mn, Co, Ni, Cu, Zn, Ge, Ga, Y, Nb, Cd, Ca, and La, each in a content of 0.01 at % to 15 at %, and/or one alloy element or a plurality of alloy elements selected from the group composed of Hf, Pb, Bi, Ru, Rh, Pd, Ag, Au, Ta, W, Re, Os, Ir, and Pt, each in a content of 0.01 at % to 5 at %.

9. The molybdenum alloy according to claim 3, additionally containing one alloy element or a plurality of alloy elements selected from the group composed of Al, Fe, Zr, Mg, Li, Cr, Mn, Co, Ni, Cu, Zn, Ge, Ga, Y, Nb, Cd, Ca, and La, each in a content of 0.01 at % to 15 at %, and/or one alloy element or a plurality of alloy elements selected from the group composed of Hf, Pb, Bi, Ru, Rh, Pd, Ag, Au, Ta, W, Re, Os, Ir, and Pt, each in a content of 0.01 at % to 5 at %.

10. The molybdenum alloy according to claim 2, wherein the proportion of silicide phases is at least 30 at %.

11. The molybdenum alloy according to claim 3, wherein the proportion of silicide phases is at least 30 at %.

12. The molybdenum alloy according to claim 4, wherein the proportion of silicide phases is at least 30 at %.

13. The molybdenum alloy according to claim 6, wherein the proportion of silicide phases is at least 30 at %.

14. The molybdenum alloy according to claim 7, wherein the proportion of silicide phases is at least 30 at %.

15. The molybdenum alloy according to claim 8, wherein the proportion of silicide phases is at least 30 at%.

16. The molybdenum alloy according to claim 9, wherein the proportion of silicide phases is at least 30 at %.

Description

(1) The alloy system according to the invention is characterized in detail below on the basis of examples and figures, in which

(2) FIG. 1 shows an x-ray diffractogram of the alloy specimen MK6-FAST (Mo-40V-9Si-8B);

(3) FIG. 2 shows the microstructure of the alloy specimen MK6-FAST according to FIG. 1 after compaction by means of the FAST method, depicted as a binary image; and

(4) FIG. 3 shows the results of the microhardness test taking into consideration the standard deviation of the alloy specimens in accordance with the examples.

(5) A) Specimen Preparation

(6) 1. Mechanical Alloying

(7) Alloys with 10, 20, 30, and 40 at % vanadium were prepared. The atomic contents of silicon (9 at %) and boron (8 at %) remain the same for all alloy systems. 30 g of each alloy system were prepared. For this purpose, the individual alloy components were weighed out under argon protective gas atmosphere and placed in a grinding vessel. The obtained powder mixtures were ground in a planetary ball mill of the company Retsch GmbH (Model PM 4000) using the following parameters:

(8) TABLE-US-00001 Speed 200 rpm Temperature 20° C. (293.15 K) Ball/powder ratio 14:1 (100 balls) Grinding time 30 hours
The obtained alloys were given the following designations:

(9) TABLE-US-00002 Designation Alloy composition MK3 Mo—10V—9Si—8B MK4 Mo—20V—9Si—8B MK5 Mo—30V—9Si—8B MK6 Mo—40V—9Si—8B
2. Heat Treatment
The alloys obtained in accordance with 1. were heat-treated.
The specimens were each placed in ceramic crucibles and annealed under argon protective gas over the entire period of heat treatment.
For this purpose, approximately 10 g of each of the alloys present in the initial state were poured out and subjected to heat treatment at 1300° C. for 5 hours in a kiln of the HTM Retz GmbH Losic model.

(10) The specimens obtained were given the following designations:

(11) MK3-WB, MK4-WB, MK5-WB, and MK6-WB

(12) 3. Preparation of an Alloy Specimen by Means of FAST

(13) The specimen MK6-WB was compacted by means of FAST. For this purpose, the specimen was placed under vacuum at a pressure of 50 MPa and a holding time of 10 minutes at 1100° C. and 15 minutes at 1600° C., whereby it was heated and cooled at 100 K/min.

(14) The obtained specimen was given the designation MK6-FAST.

(15) B) Structure Investigation

(16) 1. X-ray diffractometry (XRD)

(17) The structure investigation of the specimens MK3-WB, MK4-WB, MK5-WB, MK6-WB, and MK6-FAST, ground to powder, was carried out by means of x-ray diffraction analysis using an x-ray diffractometer system PANalytical X′pert pro:

(18) radiation: Cu-K21,21,5406 voltage: 40 kV current: 30 mA detector X′ Celerator RTMS filter: Ni filter measuring range: 20°≤2Θ≤158.95° step width: 0.0167° measuring time 330.2 s (per step width).

(19) In all five specimens, the phases Mo—V mixed crystal, (Mo,V).sub.3Si, and (Mo, V).sub.5 SiB.sub.2 were detected.

(20) The result of the analysis for MK6-FAST is depicted in FIG. 1.

(21) 2. Structure Investigation and Density Determination

(22) The microstructure and the morphology of the powder particles were analyzed using a scanning electron microscope ESEM (SEM) XL30 of the Philips company. The depiction of the phase contrasts occurred by means of BSE contrast. The obtained phases were assigned by means of EDX analysis.

(23) For the specimen preparation, small amounts of the specimen powder were embedded cold in epoxy resin as follows and then wet-ground using SiC sandpaper with grains of 800 and 1200 and polished with a diamond suspension.

(24) For the SEM investigation, the specimens were sputtered with a thin layer of gold prior to being embedded.

(25) The structure of the alloy MK6-FAST is depicted in binarized form in FIG. 2. In this case, the Mo mixed crystal phase is white and the two silicide phases are black.

(26) The density of MK6-FAST was determined by means of the Archimedes principle to be 7.8 g/cm.sup.3.

(27) C) Analysis

(28) 1. SEM/EDX Analysis

(29) The EDX analysis confirmed the results of the XRD measurement. In the structure of all specimens, the silicide phases (Mo,V).sub.3Si and (Mo,V).sub.5SiB.sub.2 have formed in addition to the Mo mixed crystal. A higher proportion of vanadium was thereby found in the silicide phases than in the mixed crystal matrix.

(30) The analysis of MK6-FAST revealed that, in comparison to the heat-treated specimens, it has the highest proportion of silicide phases in the structure.

(31) Summarized in the following table are the percent proportions (at %) of the silicide phases in the individual specimens.

(32) TABLE-US-00003 Sample Silicide phases (at %) MK3-WB 46.0 MK4-WB 47.8 MK5-WB 51.1 MK6-WB 52.6 MK6-FAST 55.4
2. Microhardness Test
The microhardness of the mechanically alloyed (MA) specimens MK3, MK4, MK5, MK6, and MK6-FAST was measured.

(33) The microhardness was determined according to the Vickers method using a microscope of the company Carl Zeiss Microscopy GmbH (Model Axiophod 2), in which a hardness tester of the company Anton Paar GmbH (Model MHT-10) was integrated: testing force: 10 p testing time: 10 s rate of rise: 15 p/s

(34) The specimens were prepared as for the SEM analysis (see B. 2), but without gold sputtering.

(35) 50 indentations per phase were applied and analyzed.

(36) The result is shown in FIG. 3 taking into consideration the standard deviation. The microhardness of the silicides in the FAST specimen is significantly higher than that in the mixed crystal phase. The very fine and homogeneous distribution of the silicide phases as well as their proportion of approximately 55% ensures a high overall hardness of the alloy. The overall hardness of the FAST specimen is composed of the respective microhardnesses of the individual phases, namely, the MoV mixed crystal phase and the two silicide phases.