GB2269182A - Titanium-base hard sintered alloy - Google Patents

Description

2269182 TITANIUM-BASE MW SINTERED ALLOY The present invention relates to a

titanium-base hard sintered alloy suitably used as a corrosion- and wear-resistant material for casting molds, pump parts, bearings, mechanical seals, valves, pipes, stirrers, mixersy and blades.

Conventional corrosion- and wear-resistant materials for the above" uses are exemplified by the cemented carbides disclosed in Japanese Unexamined Patent Publications Nos. 48-17966 and 49-20845; Stellite, high-chromium cast iron, and SUS440 stainless steel disclosed in Japanese Unexamined Patent Publications Nos. 53-125208 and 60-224732; and Ti-Nb alloy and Ti6%A1-4%V alloy disclosed in Japanese Unexamined Patent Publication No. 483837.

Wear resistance and corrosion resistance are incompatible with each other. Cemented carbides, Stellite, high-chromium cast iron,, and hard stainless steel are superior in wear resistance but not necessarily good in corrosion resistance, and hence they cannot be used under severe conditions.

Particularly, titanium alloys containing 15 to "30 wt% -molybdenum are renowned for having much higher corrosion resistance than pure titanium. Titanium alloys are superior in corr-osion resistance but insufficient in wear resistance.

A titanium alloy with improved wear resistance has appeared, which contains a carbide dispersed therein. It is produced by melting as disclosed in Japanese Unexamined Patent Publications Nos. 2-129330 and 3285034. Unfortunately, it suffers from disadvantages due to melting. Specifically, it contains carbide in the form of coarse grains, which leads to insufficient hardness and wear resistance. In addition, it requires difficult machining to be made into parts of complex shape after casting.

In order to address the above-mentioned melting problem associated with the titanium alloy, the present inventors developed one which is made by powder metallurgy, as disclosed in "journal of the Japan Society of Powder and Powder Metallurgy", vol. 22, No. 3. Their development led to a sintered alloy of Ti-30Mo (15.9 vol% Mo) and a sintered alloy of Ti-MoTiC having improved wear resistance which is obtained by incorporating the former with TiC in an amount of 10 to 35 wt% (10.1 to 37.2 vol%), as disclosed in Japanese Patent Publications Nos. 51-19403 and 54-19846.

Meanwhile, recent chemical and machine industries need titanium-base sintered alloys which, under more severe conditions than before, exhibit good wear resistance as well as high strength without any loss in the corrosion resistance inherent in titanium. This need is not met by the above-mentioned Ti-Mo-TiC sintered alloy because of its insufficient wear resistance and strength. It turned out, however, that the Ti-Mo-TiC sintered alloy does not have sufficient corrosion resistance even though the amount of TIC therein is increased.

It is an object of the present invention to provide a titanium-base sintered alloy which, owing to its increased hardness, exhibits higher wear resistance and/or strength and specific strength than the conventional one. without any loss in corrosion resistance.

The present invention is embodied in a titaniumbase sintered alloy which comprises a TIC and/or TiN or Ti(C, N) solid solution accounting for 5 to 70 vol%, with the remainder being composed of two components, the first component being at least one species selected from the group consisting of Groups Va and VIa metallic elements and their mutual solid solutions, and carbides, nitrides, and carbonitrides of Groups Va and VIa metallic elements and their mutual solid solutions, the second component being titanium, with the first component accounting for 1 to 30 vol% of the total amount of the first and second components comined.

- 3 The titanium-base sintered alloy produces a good result when the content of TIC or TIN is 37.2 to 70 vol% and the first component accounts for 1 to 15 vol% of the remainder.

According to a -preferred embodiment, the major constituent, which is TIC and/or TIN or Ti(C, N) solid solution, and the first component of the remainder, which is at least one species selected from the group consisting of Groups Va and VIa metallic elements and their mutual solid solutions, and carbides, nitrides, and carbonitrides of Groups Va and VIa metallic elements and their mutual solid solutions, are in the form of solid solution.

Fig. 1 is a graph showing how the alloy_ of the present invention varies in transverse rupture strength depending on the amount of TIC, with the Mo/(Ti+Mo) ratio remaining constant.

The titanium-base hard sintered alloy of the present invention provides high wear resistance and hardness owing to its increased content of TIC or TIN, and additionally provides high strength while maintaining good corrosion resistance owing to its composition M/(Ti+M) in a specific range where M denotes a Group Va or VIa metallic element or a solid solution thereof.

The following description is given on the assumption that the titaniumbase hard sintered alloy is composed of Ti, mo, and TiC. This sintered alloy has two phases of Ti and TiC, with Mo more resolved in the Ti phase than in the TiC phase. The amount of TiC should be properly controlled because the Ti in the Ti phase dissolves in the TiC phase, increasing the content of Mo in the Ti phase beyond what is intended. The increased Mo content lowers the transverse rupture strength, hardness, and corrosion resistance. To avoid this situation, it is necessary to decrease the amount of Mo if a large amount of TiC is to be incorporated into the alloy.

According to the present invention, the metallic element added may be in the form of carbide or nitride. In this casey the titanium-base sintered alloy contains its metallic element both in the form of a solid solution in the Ti phase in the carbide or nitride. The solid solution forms after the carbide or nitride has decomposed. As this decomposition takes a long time, the concentration of the solute (metallic element) in the Ti phase remains low. This favors a properly controlled composition with improved physical properties.

Mo, as the solute element in the Ti phase, may be partly or entirely replaced by Nby Ta, or W belonging to Group Va or VIa. Because of their smaller diffusion coefficient compared to that of Mo, the concentration of Nb, Tar or W in the Ti phase is lower than that of Mo. This prevents grain growth in the TiC or TiN phase and improves the hardness'and transverse rupture strength. The metallic elements in Groups Va and VIa have diffusion coefficients in the Ti phase at 1673K as shown below.

Mo... 1.158 X 10-12 (M2/S) Nb... 0.779 X 10-12 X 10-12 Ta... 0.272 W... 0.648 x 10-12 V... 3.214 X 10-12 Cr... 3.899 X 10-12 Incidentally, despite having greater diffusion coefficients than Mo, V and Cr provide the sintered alloy with a high degree of hardness and strength if sintering is carried out under adequate conditions. Moreover, their low specific gravity is favorable to high specific strength.

The invention will be understood more readily by reference to the following examples; howeverr these examples are intended only to illustrate the invention and should not be construed to limit the scope of the invention.

Commercial Ti powder, Mo powder, and TiC powder were mixed using an automated mortar for 1 hour according to the formulation shown in Table 1. The 2 resulting mixture was press-formed at 2000 kg/cm The compact was sintered at 1300 to 1500C for 2 hours in a vacuum atmosphere. The resulting sintered body was tested for hardness (HRC), transverse rupture strength (GPa), and corrosion resistance. The results are shown in Table 2. (Corrosion resistance is expressed in terms of the rate of the corrosion that occurs when the sample is immersed in a dry cell mix for 7 days.

0 = 0.05 mm/year or less; = 0.1 mm/year or less; X = more than 0.1 mm/year.) Table 1

Sample Composition (voi%) Sintering No. Ti Ta Cr mo W TiC Ti N Ti (C, N)' te m p. (T) Example 1 44.3 8.4 47.3 1400 2 35.8 6.8 57.4 1400 3 27.6 5.2 67.2 1400 4 44.3 8 4 47.3 1300 35.8 6.8 57.4 1300 6 27.6 5.2 67.2 1200 7 64.8 3.1 32.1 1400 8 61.1 6.8 32.1 1400 9 55.0 2.7 42.3 1400 '52.0 5.7 42.3 1400 11 50.3 2.4 47.3 1400 12 47.5 5.2 47.3 1400 13 47.5 5.2 47.3 1400 14 47.5 5.2 47.3 1400 is 45.4 2.2 52.4 1400 16 42.9 4.7 52.4 1400 17 40.6 2.0 57.4 1400 18 38.4 4.2 57.4 1400 19 36.0 1.7 62.3 1400 33.9 3.8 62.3 1400 21 31.3 1.5 67.2 1400 22 29.5 3.3 67.2 1400 23 44.3 8.4 47.3 1400 24 35.8 6.8 57.4 1400 27.6 5.2 67.2 1400 26 57.1 10.8 32.1 1400 27 48.5 9.2 42.3 1400 28 44.3 8.4 47.3 1400 29 40.0 7.6 52.4 1400 35.8 6.8 57.4 1400 31 31.7 6.0 62.3 1400 32 27.6 5.2 67.2 1400 Comp. 1 37.7 62.3 1400 Example 2 21.0 4.0 75.0 1400 3 Ti (AS No. 2) 4 Ti-6A1-4V Ti-15V-3Cr-3A1-35n-1.3C 6 Stellite #6 7 SUS304 8 WC-1.0Cr-8.0M Note: Ti(CA = Ti(C0.5, NO.5) 8 Table 2

Transverse Tensile Sample Hardness rupture strength Corosion Overall No. (HRC) strength W5) resistance rating W5) Example 1 64.3 0.78 0 @ 2 69.3 0.58 0 @ 3 58.3 0.36 0 @ 4 64.9 0.58 0 @ 68.6 0.36 0 @ 6 59.3 0.35 0 @ 7 54.0 0.78 0 @ 8 60.1 0.79 0 @ 9 59.0 0.56 0 65.4 0.67 0 11 62.2 0.51 0 12 67.5 0.58 0 13 67.8 0.62 0 14 62.6 0.49 0 00 is 64.4 0.47 0 16 68.5 0.53 0 17 65.0 0.45 0 18 68.6 0.51 0 19 65.9 0.44 0 67.5 0.47 0 @ 21 66.2 0.40 0 @ 22 64.5 0.42 0 @ 23 64.1 0.68 0 @ 24 68.9 0.56 0 @ 58.0 0.35 0 @ 26 59.2 0.75 0 0 27 64.8 0.56 0 0 28 66.4 0.44 0 0 29 67.3 0.37 0 0 66.0 0.33 0 0 31 63.3 0.29 0 0 32 60.4 0.25 0 0 Comp. 1 57.2 0.17 Example

2 53.0 0.17 0 3 24.0 0.40 0 X 4 35.0 0.93 0 X 40.0 - - 0 A 6 40.0 0.73 A X 7 10.0 0.52 < X X 8 90.0 (HRA) 2.20 X X The following is noted from Tables 1 and 2. The alloys (Sample Nos. 1 to 32) pertaining to the present invention are superior in strength and/or hardness and corrosion resistance to the alloy (Sample No. 1 for comparison) containing no Mo. They are superior in strength to the alloy (Sample No. 2 for comparison) containing a large amount of TiC. They are superior in wear resistance to the Ti-base alloys (Sample Nos. 3 to 5 for comparison). They are superior in hardness and corrosion resistance to the Stellite alloy (Sample No. 6 for comparison) and the SUS 304 (Sample No. 7 for comparison). They are far superior in corrosion resistance to the cemented carbide (Sample No. 8 for comparison).

The above amply demonstrates that the alloys of the present invention are superior in general to those in the Comparative Example.

Fig. 1 shows the relation of hardness (HRC) and transverse rupture strength (GPa) to the amount of TiC (vol%) for the alloys listed in Table 1, with the ratio of Mo/(Ti+Mo) fixed at 16 vol% or 10 vol%. The ratio of 16 vol% is valid for the alloy samples Nos. 26 to 32, and the ratio of 10 vol% is valid for the alloy samples Nos. BY 10r 12, 16, 18, 20, and 22.

It is noted that the hardness reaches its peak when the amount of TiC is around 50 to 55%j, with the maximum value being higher for the Mo/(Ti+Mo) ratio of 10 vol% than for the Mo/(Ti+Mo) ratio of 16 vol%. It is - also noted that the transverse rupture strength decreases as the amount of TiC increases, with the values of transverse rupture strength being higher for the Mo/(Ti+Mo) ratio of 10 vol% than for the Mo/(Ti+Mo) ratio of 16 vol%. This suggests that the Mo/(Ti+Mo) ratio should be low for the high TiC content so that the sample will have a high transverse rupture strength. When it comes to corrosion resistance, the samples with the Mo/(Ti+Mo) ratio of 10 vol% are superior to those with the Mo/(Ti+Mo) ratio of 16 vol%. Theref ore, the Mo/(Ti+Mo) ratio should preferably be in the range of 1 to 15 vol% so that the alloys are superior in hardness and transverse rupture strength and corrosion resistance.

Alloy samples Nos. 33 to 55 pertaining to the present invention were prepared from Ti and at least one species selected from Groups Va and VIa metallic elements and carbides, nitrides, and carbonitrides of their mutual solid solutions. Table 3 shows their composition and sintering temperature, and Table 4 shows their characteristic properties such as hardness, transverse rupture strengthy and corrosion resistance and their overall rating.

- 11 Table 3

Sample Composition (voi%) Sinterinq No.

Ti Mo VC NbC TaC TaN Cr3C2 M02C (Nb,Ta)C (Ti,Mo)C WC TiC temp. ('C) 33 54.1 11.4 34.5 1350 34 43.9 9.2 46.9 1350 33.9 7.1 59.1 1350 36 52.1 10 " 3 37.6 1400 37 42.2 8.4 49.4 1400 38 32.5 6.4 61.1 1400 39 52.1 10.3 37.6 1400 42.2 8.3 49.5 1400 41 32.5 6.4 61.1 1400 42 52.1 10.3 37.6 1400 43 52.1 10.3 37.6 1300 44 42.2 8.3 49.5 1300 32.5 6.4 61.1 1300 46 48.6 9.9 51-5 1500 47 39.4 8.0 52.6 1500 48 30.4 6.1 63.5 1500 49 42.2 8.3 49.5 1400 48.6 51.4 1400 51 36.5 5.5 6.5 5.1.5 1400 52 39.7 5.5 3.5 51.3 1400 53 53.0 10.8 36.2 1400 54 43.0 8.8 48.3 1400 33.1 6.7 60.1 1400 1 (,i k Note: (Nb, Ta)C = (Nbo.5, Tao.5)C, (Ti, Mo)C = (Ti 0.9, Mo o.l)C - 12 Table 4

Sample NO. Hardness (HRC) Strength (GPa) Corrosion Overall rating resistance 33 58.6 0.75 0 @ 34 60.4 0.50 0 @ 62.2 0.48 0 @ 36 61.2 0.66 0 @ 37 64.6 0.46 0 @ 38 60.0 0.34 0 39 63.8 0.56 0 @ 64.7 0.80 0 @ 41 68.8 0.40 0 @ 42 60.6 0.53 0 @ 43 65.0 0.56 0 @ 44 65.6 0.65 0 @ 64.0 0.41 0 46 67.5 0.42 0 47 67.6 0.39 0 48 61. 0.34 0 49 66.7 0.44 0 @ so 68.0 0.60 0 @ 51 63.2 0.48 0 52 63.4 0.47 0 53 63.5 0.78 0 54 68.1 0.68 0 @ 69.0 0.60 0 @ It is noted that the samples (Nos. 33 to 55) pertaining to the present invention are superior in hardnessr transverse rupture strength, and corrosion resistance to the comparative samples (Nos. 1 to 8). Sample No. 50 is most desirable of all.

The samples (Nos. 1 to 3, 33 to 42,, 49, 51, and 52) containing Vr Nb. and Ta outperformed other samples (Nos. 4 to 32, 43 to 48, 50, and 53 to 55) not containing these elements and the comparative samples (Nos. 1 to 8) when immersed in a boiling 50% nitric acid mixture.

Moreover, the samples (Nos. 1 to 3, 36 to 42, 49, 51, and 52) containing Nb and Ta were two to five times better than other samples (Nos. 4 to 35, 43 to 48, 50 and 53 to 55) not containing these elements and the comparative samples (Nos. 1 to 8) in oxidation resistance tested by heating in the atmosphere at 800 to 9000C for 1 hour.

It is concluded from the foregoing that the alloys pertaining to the present invention exhibit improved strength and wear resistance without loss in corrosion resistance, and that the best result is produced when they contain TiC, TiN, or Ti(C, N) in an amount of 35 to 70 vol% and contain Mo such that the ratio of Mo/(Ti+Mo) is within the range of 1 to 15 vol%.

According to the present invention, the following effects will be exhibited:

(1) The alloy exhibits improved strength, wear resistance, and specific strength, while retaining the good corrosion resistance inherent in titanium. (2) The alloy composed of Ti-(Cr, V)-TiC is superior in strength (specific strength) to the conventional Ti-Mo-TiC alloys. It is suitable for corrosion- and wear-resistant parts subjected to severe conditions.

(3) The alloy composed of Ti-(V, Nb, Ta)-TiC is far superior in corrosion resistance (especially to hot nitric acid), It will f ind use in nuclear fuel treatment plants.

(4) The alloy composed of Ti-(Nb, Ta)-TiC is superior in oxidation resistance. It will find use in power plants where parts are exposed to hot corrosive gases, (5) The alloy containing TiC, TiN, or Ti (C, N) in an amount of 35 to 70 vol% and containing Mo such that the ratio of Mo/(TI+Mo) is within the range of 1 to 15 vol% is particularly superior in strength, corrosion resistance, wear resistance. It is more durable than the conventional alloys under severe conditions.

(6) The alloy will find use in corrosion- and wearresistant parts such as molds (to form dry cell mix), pumps, bearings, mechanical seals, valves, pipes, stirrers, mixers, and blades in the chemical and machine industries. Its outstanding properties extend the life of parts, reduce the frequency of part changes, and lessen the amount of required maintenance.

(7) The alloy will meet requirements for operation under severe conditions and contribute to improved operating efficiency.

Claims (4)

1. A titanium-base sintered alloy which comprises TiC and/or TiN or Ti(C, N) solid solution in an amount of 5 to 70 vol%, with the remainder being composed of two components, the first component being at least one species selected from Groups Va and VIa metallic elements and their mutual solid solutions, and carbides, nitrides, and carbo-nitrides of Groups Va and VIa metallic elements and their mutual solid solutions, and the second component being titanium, the first component being in an amount of 1 to 30 vol% of the total amount of the first and second components.

2. A titanium-base sintered alloy as claimed in Claim 1,,wherein the major constituent, which is TiC and/or TiN or Ti (C, N) solid solution, and the said first component of the remainder, are in the form of solid solution.

3. A titanium-base sintered alloy as claimed in Claim 1 or 2, wherein the content of TiC or TiN is 35 to 70 vol%, and the first component accounts for 1 to 15 vol% of the remainder.

4. A titanium-base sintered alloy substantially as herein described in any of the foregoing Examples 1 to 55.

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