JP5630876B2 - Heat-resistant PtRh alloy - Google Patents

Description

  The present invention relates to a heat-resistant PtRh alloy used in a high temperature region such as energy-related members, members for aerospace industry, structural materials for manufacturing high melting point materials.

  Platinum group elements used for heat-resistant materials are known as Pt, Ir, and Rh. Among them, Pt is in the form of pure Pt, Pt alloy, reinforced Pt, etc. It is widely used industrially as electrical materials such as structural materials, thermocouples and heater wires, temperature sensors, and electrodes for spark plugs. The typical reason is that among a number of metals, the melting point is relatively high and the vapor pressure is low, so that it is difficult to wear out, hardly oxidize, and has high chemical stability.

Pure Pt and reinforced Pt can be used at high temperatures regardless of the atmosphere such as vacuum, inert atmosphere, air, and the like. However, in a reducing atmosphere, contact with light elements such as phosphorus, lead, arsenic, boron, bismuth, silicon, and zinc reacts at a low temperature of about 400 to 500 ° C to form an alloy, causing melting point drop and embrittlement. May lead to destruction.
In addition, since pure Pt and reinforced Pt have a melting point of 1769 ° C., heat resistance may be insufficient at a high temperature of 1500 ° C. or higher. In that case, it is used by alloying with an element having a high melting point, and specifically, a PtRh alloy that is resistant to oxidation consumption is often used. The PtRh alloy has a higher melting point than that of pure Pt or reinforced Pt due to alloying, and can increase the normal temperature. However, in a reducing atmosphere, as with pure Pt and reinforced Pt, it reacts with light elements such as phosphorus, lead, arsenic, boron, bismuth, silicon, and zinc, causing abnormalities such as melting point drop and embrittlement. It is clear from the phase equilibrium diagram that the melting point of alloys of Pt and these light elements is extremely low compared to Pt. Such attention is disclosed in Non-Patent Document 1, for example.

  On the other hand, there is Patent Literature 1 as a disclosure of the technology related to the PtRh alloy. This technology is an electrode material with 0.5 to 5.0 mass% W, 1.0 to 20.0 mass% Rh, and the balance Pt, and prevents a decrease in tensile strength after heat treatment at 1000 ° C or higher compared to conventional PtRh alloys. In order to prevent breakage during use, the strength is improved.

  Patent Document 2 discloses a bushing for glass fiber using a heat-resistant alloy containing 75 to 96 mass% of Pt, 1 to 20 mass% of Rh, and 3 to 5 mass% of Ru and / or Ir as a heat-resistant alloy. It is disclosed. This technology is intended to solve the problems that conventional PtRh alloys have low high-temperature creep strength and that reinforced Pt has a Vickers hardness that is too high to form a bushing.

Platinum Metals Review, 1958, 2 (4), pp. 120-123 JP-A-53-51124 JP 2003-48741 A

  PtRh alloy has been widely used as a heat-resistant material, and many technological developments have been made to improve mechanical properties such as high-temperature strength, but light elements such as phosphorus, lead, arsenic, boron, bismuth, silicon, and zinc. Although there was a need to improve the corrosion resistance of heat-resistant alloys, the point that caused abnormalities due to contact with the steel has not been noticed until now. Anomaly caused by contact between PtRh alloy and light element is that light element that contacts PtRh alloy in a reducing atmosphere or low oxygen partial pressure atmosphere diffuses along the metal surface and internal grain boundaries, and is a low melting point alloy with Pt. Happens to produce.

  Therefore, the present invention aims at providing a heat-resistant PtRh alloy that is resistant to corrosion by P, in particular, to improve the corrosion resistance still insufficient in the conventional PtRh alloy.

  As a result of intensive studies to achieve the above problems, the present inventors have determined that PtRh has a Re of 1.0 to 5.0 mass%, a W of 1.0 to 5.0 mass%, an Ir of 1.0 to 5.0 mass%, and a Ru of 0.3. The present invention was completed by containing at least one of ˜5.0 mass%, further setting Rh to 20 to 40 mass% and the balance to Pt.

  The alloy of the present invention is a PtRh alloy, wherein Re is 1.0 to 5.0 mass%, W is 1.0 to 5.0 mass%, Ir is 1.0 to 5.0 mass%, Ru is 0.3 to 5.0 mass%, Re, W, Ir And at least one element of Ru, Rh being 20 to 40 mass% and the balance being Pt.

  The reason for limiting the range of Re and W to 1.0 to 5.0 mass% is that if it is less than 0.1 mass%, sufficient corrosion resistance cannot be obtained when contacting with phosphorus, and if it exceeds 5.0 mass%, it is disadvantageous for heat resistant materials. This is because the oxidization and volatilization in the high temperature region becomes intense.

  The reason for limiting the range of Ir to 1.0 to 5.0 mass% is that if it is less than 0.3 mass%, sufficient corrosion resistance cannot be obtained when contacting with phosphorus, and if it exceeds 5.0 mass%, it is disadvantageous for heat resistant materials This is because oxidation and volatilization in a high temperature region becomes intense.

  The reason for limiting the range of Ru to 0.3-5.0 mass% is that if it is less than 0.3 mass%, sufficient corrosion resistance cannot be obtained when contacting with phosphorus, and if it exceeds 5.0 mass%, it is disadvantageous for heat-resistant materials This is because oxidation and volatilization in a high temperature region becomes intense.

  The reason for limiting the Rh range to 20 to 40 mass% is that if it is less than 10 mass%, sufficient corrosion resistance cannot be obtained when contacting with phosphorus, and if it exceeds 40 mass%, the alloy becomes brittle and the workability is reduced. This is to make it happen.

The alloy having the above composition is resistant to corrosion by phosphorus and has sufficient heat resistance, thus improving the reliability of structural materials such as melting crucibles and appliances and electrical materials such as thermocouples and heater wires, and its durability. Can increase the sex.
Of the alloys having the above composition, when a PtRh alloy containing Re and Rh is used, it can be strong against corrosion caused not only by phosphorus but also by Pb.

  This will be specifically described below.

Cross section of the reference example alloy ( reference example 12 ) after the phosphorus resistance test Cross section of conventional alloy (Comparative Example 1) after phosphorus resistance test Graph showing the relationship between the Rh addition amount and phosphorus resistance of the reference alloy (1.0Cr-added PtRh alloy) Graph showing the relationship between the amount of added elements and phosphorus resistance Graph showing lead resistance of reference alloy and conventional alloy

(Sample preparation)
An ingot of a PtRh alloy having the composition shown in Table 1 was obtained by blending raw metal in a predetermined amount and melting it in an arc melting furnace. Rolling and heat treatment were repeatedly performed to obtain a constant processing rate, and processing was performed to a plate thickness of 0.5 mm. Finally, it was punched into a predetermined shape by press working to obtain a test piece, which was evaluated by the following test methods.
For melting the ingot, means such as a vacuum melting furnace and a plasma melting furnace can be used.

(Hardness test)
In the hardness test, the processed material and the annealed material of the test piece were each subjected to a load of 200 gf and a load application time of 10 seconds using a micro Vickers hardness tester.

(Phosphorus resistance test)
In the phosphorus resistance test, the test piece and red phosphorus prepared by the above method were sealed in a heat-resistant container, and the cross section of the test piece after heat treatment in an inert gas at 800 ° C. for 1 hour was observed with a metal microscope. Phosphorous resistance is defined by Formula 1, and the higher the value, the higher the corrosion resistance.
Formula 1: Phosphorus resistance (%) = thickness of unreacted portion / cross-sectional thickness of test piece × 100

(Oxidation volatility test)
The mass before the test of the test piece produced by the above method was measured, and the mass of the test piece after heat treatment for 20 hours in an electric furnace at 1200 ° C. in the atmosphere was measured. The mass change of the test piece was obtained by Equation 2, and the oxidation volatility was evaluated. A minus represents a mass decrease due to oxidation volatilization, and a plus represents an oxidation increase.
Formula 2: Mass change (%) = (mass after test−mass before test) / mass before test × 100

(Lead resistance test)
In the lead resistance test, the test piece produced by the above method was immersed in molten lead glass in an electric furnace at 800 ° C., held for 8 hours, taken out, and the cross section of the test piece was observed with a metal microscope. The thickness of the reaction layer with lead appearing in the cross-sectional surface layer was measured, and the lead resistance was evaluated by Equation 3. Lead resistance here is the ratio of the thickness of the reaction layer with the conventional alloy (Comparative Example 1), and the lower the value, the better the corrosion resistance.
Formula 3: Lead resistance = (reaction layer thickness with lead of test piece) / (reaction layer thickness with lead of Comparative Example 1)

(result)
The results of the test are shown in Table 2.
All of the reference example alloys were more excellent in phosphorus resistance than the comparative example alloys except comparative example 7.

The PtRh alloy of the reference example had a thinner reaction layer than the conventional PtRh alloy (Comparative Example 1), and effectively suppressed the reaction with phosphorus. An example is shown in FIG. In contrast, Comparative Example 1 and Comparative Example 2 known as reinforced Pt, and further Comparative Examples 3 to 6, reacted significantly with phosphorus, and a thick reaction layer was formed. An example is shown in FIG. Also in pure Pt, a thick reaction layer was observed as in FIG.

In the PtRh alloy of the reference example, the amount of Rh added was 10 mass% or more, and the phosphorus resistance was increased to 50% or more (FIG. 3).

In the PtRh alloy of the reference example , although there was a slight difference in the effect of increasing the phosphorus resistance depending on the type and amount of the additive element, the phosphorus resistance increased to 30% or more in all cases.
Conventional PtRh alloys (Comparative Example 1) and alloys with compositions outside the scope of the present invention (Comparative Examples 2 to 6) are inferior in phosphorus resistance to the reference examples , and depending on the type and amount of elements added to Pt, Some of them deteriorated phosphorus resistance (Table 2 and FIG. 4).

The change in the mass of the PtRh alloy of the reference example showed an increase or decrease, but the amount was as small as ± 0.1%, which was not so high as to cause problems in high temperature use.
Although the mass change of the alloys of Comparative Examples 1 to 6 was as small as that of the Reference Example , Comparative Example 7 was greatly reduced to −0.58% and the oxidation volatilization was severe.

Of PtRh alloy of Reference Example, Reference Example 2, Reference Example 5, Reference Example 12, Reference Example 24, not only excellent in phosphorus as compared to the conventional example alloy was superior to耐鉛(Figure 5) .

Claims (3)

For PtRh alloys, Re is 1.0 to 5.0 mass% (excluding 1.0%) , W is 1.0 to 5.0 mass% (excluding 1.0%) , Ir is 1.0 to 5.0 mass% (excluding 1.0%) , Ru Is a heat-resistant PtRh alloy characterized by containing at least one of 0.3 to 5.0 mass%, Rh of 20 to 40 mass% (excluding 20%) and the balance being Pt.   A structural material comprising the alloy according to claim 1.   An electrical material comprising the alloy according to claim 1.