JP2010031310A - White gold alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a white gold alloy in which embrittlement caused by overaging is suppressed while improving its hardness. <P>SOLUTION: Disclosed is the white gold alloy composed of an Au alloy obtained by adding, to 75 to 77 mass% Au, 10 to 17 mass% Cu and 0.01 to 0.5 mass% Ru, and, as necessary, 0.1 to 2.0 mass% Ga, and the balance Pd. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention belongs to the technical field of white gold alloys in which 75 to 77 mass% Au and Cu are 10 to 17 mass%, Ru is 0.01 to 0.5 mass% and the balance is Pd.

As a method for producing a white gold alloy, Ni was effective as an element for improving the color tone and hardness because a certain amount of Ni was added to Au to make the color tone white and improve the mechanical properties. However, the allergy problem caused by Ni becomes remarkable, and a white gold alloy not containing Ni has been developed as in Patent Document 1.
JP-A-9-184033

  Pd is effective as an element to make the color tone white in addition to Ni, but Pd does not provide sufficient hardness compared to Ni, and it is easy to be scratched. There was a problem that was not suitable for use in various places.

As a method of improving the hardness without adding Ni, there is a method of adding Cu and depositing an ordered lattice such as Au ₃ Cu. This is improved in hardness by heat treatment at a regular temperature, for example, a relatively low temperature of 200 to 400 ° C.
However, when this temperature range is produced by a conventional casting method such as the lost wax method, depending on the cooling rate of the investment material, it may be maintained at a regularized temperature, causing overaging, and breaking when taking out from the investment material. There is. In particular, fractures often occur from grain boundaries. Since jewelry and jewelry have various shapes, the size of the investment material varies, and the cooling rate changes. Therefore, it is desired to reduce breakage due to overaging.

In order to improve the hardness without adding Ni, there is a method of depositing a regular lattice such as Au ₃ Cu, but simply adding Cu to Au causes embrittlement due to overaging, and grain boundaries There are many cases where breakage occurs as a starting point.

  The inventors of the present application have conducted extensive research to solve the above-described conventional problems, and as a result, by adding a small amount of Ru, the crystal grains are made fine, thereby reducing the breakage from the grain boundaries. A gold alloy could be obtained.

In the present invention, in Au, Ru is 0.01 to 0.5 mass%, Cu is 10 to 17 mass%, and the balance is Pd.By precipitation strengthening, the hardness is improved and the crystal grains are made finer. Reduce grain boundary fracture.
Further, by adding Ga, it is possible to improve hardness without contributing to overaging, and to obtain higher hardness.

  While adding 75 to 77 mass% Au, Cu to 17 to 17 mass%, Ru to 0.01 to 0.5 mass%, and in some cases Ga to 0.1 to 2.0 mass%, while improving the hardness by precipitation strengthening, It is possible to obtain a white gold alloy that makes crystal grains fine and suppresses breakage from grain boundaries.

The present invention is a white gold alloy containing Ru of 0.01 to 0.5 mass%, Cu of 10 to 17 mass%, and the balance of Pd in 75 to 77 mass% Au.
Specifically, if the amount of Ru added is less than 0.01 mass%, the effect of crystal grain refinement cannot be obtained, and if it exceeds 0.5 mass%, Ru segregation is likely to occur, and the color of the segregated portion is different from the surroundings, causing discoloration. This is because it looks like.
Further, if the amount of Cu added is less than 10 mass%, precipitation strengthening cannot be obtained, and if it exceeds 17 mass%, embrittlement tends to occur due to overaging.

The present invention is characterized by a white gold alloy containing 75 to 77 mass% Au, 0.01 to 0.5 mass% Ru, 10 to 17 mass% Cu, 0.1 to 2.0 mass% Ga, and the balance being Pd. .
Specifically, if the amount of Ru added is less than 0.01 mass%, the effect of crystal grain refinement cannot be obtained, and if it exceeds 0.5 mass%, Ru segregation is likely to occur, and the color of the segregated portion is different from the surroundings, causing discoloration. This is because it looks like.
Further, if the amount of Cu added is less than 10 mass%, precipitation strengthening cannot be obtained, and if it exceeds 17 mass%, embrittlement tends to occur due to overaging.
This is because when Ga addition amount is less than 0.1 mass%, the hardness is not improved, and when it exceeds 2.0 mass%, it becomes brittle and cannot be processed.

  Specific examples of the present invention will be described below.

  For the Au alloys having the respective component compositions of Examples 1 to 5 and Comparative Examples 1 to 5 shown in Table 1, workability, hardness, an embrittlement investigation accompanying the hardening treatment, an average crystal grain size, and a color tone were investigated.

  Table 2 shows the workability, the hardness after the softening treatment, and the hardness after the hardening treatment.

As shown in Table 2, all examples could be rolled up to t0.5 mm.
In Comparative Example 4 in which Ga exceeded 2.0 mass%, cracking occurred in one pass and rolling was not possible.
Thereafter, the characteristic investigation of Comparative Example 4 is not performed.

In order to examine the effect of age hardening, the difference ΔHV between the hardness after the curing treatment and the hardness after the softening treatment was calculated. The calculation method is shown in Formula 1.
In addition, in order to investigate overaging, a t0.5 mm × w5 mm × L20 mm plate after the curing treatment was bent 90 ° and a breakage test was conducted to check for breakage.
The results are shown in Table 3.

  Formula 1: ΔHV = hardness after curing (HV) −hardness after softening (HV)

As can be seen from Table 3, in Examples 1 to 5, the hardness increased after the curing treatment, and there was no defect in the fracture test.
It can be seen that when the added amount of Cu is less than 10 mass% as in Comparative Example 2, the hardness does not improve and age hardening does not occur.
In Comparative Example 1 in which Ru is not added and in Comparative Example 3 in which the added amount of Cu exceeds 17 mass%, the increase in hardness is remarkable, but in the fracture test, in Comparative Example 1, some cracks are observed at the bent portion. Occurrence, broken in Comparative Example 3.
From this, it was found that when Ru is not added or when the amount of Cu exceeds 17 mass%, embrittlement tends to occur during age hardening.

If the grain size is coarse, it often breaks along the grain boundaries, and fine grains are required. The average of the softened material that is water-cooled at 700 ° C for 15 min after 50% rolling of the sample in Table 1 The crystal grain size was examined.
The method for obtaining the average crystal grain size is shown in Formula 2.
The results are shown in Table 4.

Equation 2: D = 2 × _{[A / [π (μ 1 +} (μ 2/2))] ] ^0.5
D: Average crystal grain size
A: Measurement area
μ ₁ : Number of crystal grains not in contact with the measurement edge existing in the measurement area
μ ₂ : Number of crystal grains in contact with the measurement edge existing within the measurement area

  In Comparative Example 1 in which Ru is not added, the average crystal grain size is 50 μm, whereas in Examples 1 to 5 in which Ru is added, the average crystal grain size is 16 to 25 μm, and the average crystal grain size is less than half. The effect of addition was confirmed.

In Comparative Example 5, there was a portion where the color tone was partially different, and surface analysis by EPMA was performed.
The results are shown in FIG.

  As can be seen from the results in FIG. 1, Ru segregation was confirmed, and it was found that segregation is likely to occur when the amount of Ru added exceeds 0.5 mass%.

In order to investigate the color tone, Examples 1 to 5 rolled to about 0.5 mm were mirror-finished with emery paper and diamond paste having an average particle diameter of 1 μm, and then the color was measured by the CIEL ^* a ^* b ^* method.
The meaning of L ^* a ^* b ^* is shown below.

L ^* = lightness (larger value means brighter)
a ^* = + red / -green (the larger the value, the stronger the red and the minus the green)
b ^* = + yellow / -blue (the larger the value, the stronger yellow, and the minus value-stronger blue)

  The measurement conditions were illumination / field of view: D65 / 10 °.

The color difference ΔE ^* value from the Rh plating material was determined by the above measurement method.
Equation 3 shows how to obtain ΔE ^* .

Formula 3: ΔE ^* = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^0.5
Rh plating value: L ^* 87.55, a ^* 1.18, b ^* 2.68
ΔL ^* = (sample measurement value-87.55)
Δa ^* = (sample measurement value-1.18)
Δb ^* = (sample measurement value-2.68)

The definition of white in this case is ΔE ^* = 14 or less.

From the results in Table 5, it was confirmed that Examples 1 to 5 were ΔE ^* = 14 or less.

  As explained above, 75 to 77 mass% Au is added to Cu from 10 to 17 mass%, Ru is added from 0.01 to 0.5 mass%, and in some cases, Ga is added from 0.1 to 2.0 mass%, and the balance is made of Pd. According to the present invention, which is characterized in that, it is possible to obtain a white gold alloy that refines crystal grains and suppresses breakage from grain boundaries while improving hardness by precipitation strengthening. It was.

It is a figure which shows the surface analysis result by EPMA of the comparative example 5.

Claims (2)

  White gold alloy with 75 to 77 mass% for Au, 10 to 17 mass% for Cu, 0.01 to 0.5 mass% for Ru, and the balance of Pd.   White gold alloy with 75 to 77 mass% for Au, 10 to 17 mass% for Cu, 0.01 to 0.5 mass% for Ru, 0.1 to 2.0 mass% for Ga, and the balance of Pd.