PROCESS FOR PREPARING A TUBULAR ARTICLE

Abstract

The present invention relates to a process for preparing a tubular article, comprising (a) providing a carrier tube, (b) providing a metal coating on the carrier tube by applying a liquid metal phase onto the carrier tube and solidifying the liquid metal phase, (c) applying a contact pressure to the metal coating by at least one densification tool, and moving the densification tool and the metal coating relative to each other.

Claims

1. A process for preparing a tubular article, comprising (a) providing a carrier tube, (b) providing a metal coating on the carrier tube by applying a liquid metal phase onto the carrier tube and solidifying the liquid metal phase, (c) applying a contact pressure to the metal coating by at least one densification tool, and moving the densification tool and the metal coating relative to each other.

2. The process according to claim 1, wherein the carrier tube is made of a steel alloy, which is preferably non-magnetic; and/or wherein the carrier tube has a length of at least 500 mm.

3. The process according to claim 1, wherein the carrier tube comprises a bonding layer, and/or wherein the outer surface of the carrier tube is subjected to a surface-roughening.

4. The process according to one claim 1, wherein the liquid metal phase is applied onto the carrier tube by spraying, melt dipping, pouring a metal melt on the carrier tube, or fixing a metal wire or strip on the carrier tube and melting the metal wire or strip while rotating the carrier tube.

5. The process according to claim 1, wherein the metal is ductile, and/or the metal is a metal which is plastically deformable at room temperature.

6. The process according to claim 1, wherein the metal is indium or an alloy thereof, zinc or an alloy thereof, tin or an alloy thereof, lead or an alloy thereof.

7. The process according to claim 1, wherein the contact pressure is above the yield point of the metal coating; and/or the contact pressure is increased during step (c).

8. The process according to claim 1, wherein the 10 densification tool and the metal coating are moved relative to each other by rotation or in longitudinal direction of the carrier tube axis or a combination thereof.

9. The process according to claim 1, wherein the path of the 15 densification tool over the metal coating is spiral.

10. The process according to claim 1, wherein step (c) comprises a rolling, forging, and/or swaging.

11. The process according to claim 10, wherein the rolling is a skew rolling, a pilger step rolling, a cross rolling, a longitudinal rolling, or a combination of at least two of these rolling methods; and/or wherein the swaging is a rotary swaging.

12. The process according to claim 1, wherein the inner diameter of the carrier tube remains substantially constant during step (c).

13. The process according to claim 1, wherein step (c) starts after having finished step (b), or wherein step (c) starts while step (b) is still carried out.

14. The process according to claim 1, wherein the tubular article is a tubular sputtering target.

15. A tubular article, which comprises a carrier tube and at least one metal coating on the carrier tube, and which is obtainable by the process according to claim 1.

16. The tubular article according to claim 15, wherein the metal coating on the 10 carrier tube is continuous, non-segmented over a length of at least 500 mm, more preferably at least 1000 mm in axial direction of the carrier tube, the metal coating preferably having a relative density of at least 90%.

17. The tubular article according to claim 15, wherein the metal coating has 15 no pores with a diameter of at least 50 gm and/or the relative intensities of the four most intensive X-ray diffraction peaks of the metal coating deviate by less than 20%, more preferably less than 15% from the relative intensities of the corresponding X-ray diffraction peaks of a randomly orientated reference material of the same metal.

Description

EXAMPLES

I. Measuring Methods

[0108] Unless indicated otherwise, the parameters of the present invention have been determined by the following measuring methods:

Pore Diameter

[0109] Pore diameter was determined on a microsection which was prepared as follows: Sample was vacuum-embedded in a polymer matrix and polished with grinding papers of increasing fineness, finally polished with a 4000 SiC paper. Measuring via line intercept method (DIN EN ISO 643), the mean pore diameter was determined according to the following equation:

M=(L*p)/(N*m)

wherein
L is the length of the measuring line,
p is the number of measuring lines
N is the number of intersected pores,
m is the magnification

Number of Pores Per Volume

[0110] is determined via image-based analysis. Microsections have been taken and the number of pores on each microsection is determined. From 2D to 3D is concluded by taking average values of 30 microsections while grinding approx. 50-100 m stepwise into the depth of the material.

Relative Density

[0111]
Relative density (%)=(geometric density/theoretical density)100

Geometric density=mass/volume (geometric)

[0112] The mass of a sample is determined by weighing. The dimensions of the sample are measured with a calliper (accuracy: 0.2 mm) and the volume is calculated from the measured dimensions. Average value of three measurements is taken as the geometric density.

[0113] Theoretical density values are taken from tables of standard text books.

Porosity

[0114]
Porosity (%)=100[(geometric density/theoretical density)100]=100relative density (%)

Mean Grain Size

[0115] Grain size was determined on a microsection which was prepared as follows: Sample was vacuum-embedded in a polymer matrix and polished with grinding papers of increasing fineness, finally polished with a 4000 SiC paper. Measuring via line intercept method (DIN EN ISO 643). The mean grain size was determined according to the following equation:

M=(L*p)/(N*m)

wherein
L is the length of the measuring line,
p is the number of measuring lines
N is the number of intersected grains,
m is the magnification

Surface Roughness

[0116] Surface roughness has been measured with the optical profilometer New View 7300 of ZYGO. The measurement is based on white light interferometry and is carried out contact-free on 3D surfaces. The measuring and evaluation software Mx has been used and provides a statistical error of +/20% of the measured values. The arithmetical average of measurements at three different locations (one measurement per location) is taken as the surface roughness.

Oxygen Content

[0117] The oxygen content was determined by carrier gas hot extraction using the TC 436 apparatus from Leco. Oxygen content was determined indirectly by converting the oxygen into CO.sub.2 and capturing the CO.sub.2 in an IR measuring cell. The method is based on the ASTM E1019-03 norm. The apparatus was calibrated using a known quantity of CO.sub.2. The calibration was checked by measuring the oxygen content of a certified steel standard with a known oxygen content which was approximately equal to the oxygen content expected for the sample. The sample was prepared by weighing 100-150 mg of the material into a tin capsule. The probe was introduced at 2000 C., together with the tin capsule, into a graphite crucible, which had been degassed for about 30 seconds at 2500 C. The oxygen of the sample reacted with the carbon of the graphite crucible to yield carbon monoxide (CO). The carbon monoxide was then oxidized to CO.sub.2 in a copper oxide column. The column was held at a temperature of 600 C. The CO.sub.2 generated in this manner was then detected using an infra-red cell, and the oxygen content was determined. Before the sample was measured, a reference value was determined for an unfilled tin capsule under the same conditions. This reference value was automatically subtracted from the value determined for the sample (metal sample plus tin capsule).

X-Ray Diffraction

[0118] X-ray diffraction measurements were made on the two circle goniometer Stadi P from Stoe using Bragg-Brentano geometry. Measured with CuK1 radiation, 2 range of from 10 to 105, step width: 0.032.

[0119] The measurements were made on 10 mm*10 mm*8 mm samples, separated from the metal coating by a cutter.

[0120] In the measured diffractogram, relative intensity of an X-ray diffraction peak is determined as follows:

[0121] Ratio of the intensity (taken as peak height) of said peak to the intensity of standard values of hkl planes, multiplied by 100.

[0122] For each of the 4 most intensive diffraction peaks in the measured diffractogram, the relative intensity was compared with the relative intensity of the corresponding diffraction peak of the randomly orientated reference.

[0123] As already mentioned above, X-ray diffraction data can be taken from a commonly accessible powder diffraction file database.

II. Preparation of Tubular Sputtering Targets

Example 1: Preparation of a Tubular Sputtering Target Containing an Indium Coating

Providing an Indium Coating on a Carrier Tube

[0124] Highly pure indium (99.999%) was melted in a crucible (electrically heated). A carrier tube (stainless steel, outer diameter: 133 mm, length: 3800 mm) provided with a rough adhesion-promoting layer NiTi was mounted on a rotary device. The melted indium metal, i.e. the liquid metal phase, was supplied by a feed line to an atomizer nozzle where it was sprayed by the action of a gas. The liquid drops hit the rotating carrier tube and solidify, and a relative motion of the carrier tube versus the spray nozzle caused a thick (9 mm) metallic indium layer, i.e. the metal coating, to be deposited in the form of multiple layers on the carrier tube over time. A non-segmented metal coating was obtained (i.e. no gaps in circumferential direction). The density of the metal coating was about 80% of the theoretical density. The metal coating had a porosity of about 20%.

Densifying the Metal Coating by Applying a Contact Pressure with a Densification Tool

[0125] As shown in FIG. 1, two rolls were pressed against the rotating carrier tube. The rolls were acting as densification tools. Each roll had a diameter of 80 mm, and a length of 50 mm. In the beginning of the densification step, a contact pressure of about 0.7 MPa was applied by each of the rolls to the metal coating. This contact pressure was above the yield point of the indium coating and therefore sufficient for plastically deforming the indium coating. Due to the plastic deformation, thickness of the metal coating was reduced during step (c). As a consequence thereof, porosity of the metal coating was reduced, while density of the metal coating was increased during step (c). For making sure that the metal coating is still plastically deformed while its density is increasing, the contact pressure applied by the rolls was increased during step (c) from 0.7 MPa to a maximum value of 1.5 MPa.

[0126] In addition to the rotation about its tube axis, the carrier tube was also moved along its tube axis. Both the rotation and the movement along the tube axis contributed to the overall relative movement between the rolls and the metal coating. Accordingly, the path of each roll over the metal coating was a spiral path. The rotating carrier tube was moved along its tube axis back and forth five times. Accordingly, there were several repetitions of the spiral path of the densification tools over the metal coating, and a densified metal coating having a porosity of 4% was obtained. The density of the metal coating increased from 80% to 96% of its theoretical density. The densified metal coating did not contain pores with a diameter of more than 50 m. A micrograph of the metal coating (magnification factor: 200) is shown in FIG. 2.

[0127] The densified metal coating was subjected to an X-ray diffraction measurement. The X-ray diffractogram is shown in FIG. 3. The relative intensities of the 4 most intensive diffraction peaks are shown below in Table 1. Also listed in Table 1 are the relative intensities of the same X-ray peaks of a reference indium sample with random grain orientation.

TABLE-US-00001 TABLE 1 Relative intensities of diffraction peaks Indium coating Reference indium Deviation from of Example 1 with random the relative 2 Relative orientation intensity of Peak Value Intensity Relative Intensity reference material 101 32.97 100.0 100.0 0% 110 39.17 36.0 37.2 3.3% 112 54.48 24.0 21.5 10.4% 211 67.03 23.0 20.1 12.6%

[0128] As already mentioned above, relative intensities of X-ray diffraction peaks are very sensitive to texture modifications. Typically, if metals are subjected to a metal-forming treatment such as rolling or forging, the grain lattice planes are not randomly distributed but have a specific orientation which is favoured over other orientations. This would be reflected by a significant change of relative intensities of the X-ray diffraction peaks, if compared to a reference sample of the same metal having a random orientation. In step (c) of the process of the present invention, a contact pressure is applied to a metal coating by rolls. However, very surprisingly, the densified metal coating prepared in step (c) still has a grain structure of high randomness, as demonstrated by the X-ray diffraction data.

Example 2: Preparation of a Tubular Sputtering Target Containing a Tin Coating

[0129] a) Providing a Tin Coating on a Carrier Tube by Melt Spraying

[0130] Highly pure tin (purity: 99.9%) was melted in a crucible. Following the procedure as described in Example 1, a tin coating was provided on the carrier tube by spraying. A non-segmented tin coating was obtained (i.e. no gap in circumferential direction). The density of the metal coating was about 75% of the theoretical density. The metal coating had a porosity of about 25%.

[0131] b) Providing a Tin Coating on a Carrier Tube by Wire Arc Spraying

[0132] Wire arc spraying is done with Sn on a SST tube, coated with 100 m AlTi bond coat. The Sn wire, 99.8% purity is sprayed by Smart Arc Oerlikon Metco with 15 kg/h; 300 Ampere. After reaching 10 mm Sn layer thickness, the density of said Sn layer was about 85% of the theoretical density. Accordingly, the Sn layer had a porosity of about 15%.

Densifying the Metal Coating by Applying a Contact Pressure with a Densification Tool

[0133] Following the procedure as described in Example 1, the sprayed tin coating was subjected to a densification treatment by rolling.

[0134] In the beginning of the densification step, a contact pressure of about 3.8 MPa was applied by each of the rolls to the metal coating. For making sure that the metal coating is still plastically deformed while its density is increasing, the contact pressure applied by the rolls was increased during step (c) to a maximum value of 8 MPa.

[0135] After 10 repetitions of the spiral path of the densification tools over the metal coating, a densified metal coating having a porosity of 5% for 2a and 6% for 2b was obtained. The density of the metal coating was 95% of its theoretical density in case of 2a and 94% in case of 2b. The densified metal coating did not contain pores with a diameter of more than 50 m in both cases.

Example 3: Preparation of a Tubular Sputtering Target Containing a Lead (Pb) Coating

Providing a Lead Coating on a Carrier Tube

[0136] Highly pure Pb was melted in a crucible. Following the procedure as described in Example 1, a lead coating was provided on the carrier tube by spraying. A non-segmented tin coating was obtained (i.e. no seams in circumferential direction). The density of the metal coating was about 75% of the theoretical density. The metal coating had a porosity of about 25%.

Densifying the Metal Coating by Applying a Contact Pressure with a Densification Tool

[0137] Following the procedure as described in Example 1, the sprayed lead coating was subjected to a densification treatment by rolling.

[0138] In the beginning of the densification step, a contact pressure of about 4 MPa was applied by each of the rolls to the metal coating. For making sure that the metal coating is still plastically deformed while its density is increasing, the contact pressure applied by the rolls was increased during step (c) to a maximum value of 8 MPa.

[0139] After 10 repetitions of the spiral path of the densification tools over the metal coating, a densified metal coating having a porosity of 5% was obtained. The density of the metal coating was 95% of its theoretical density. The densified metal coating did not contain pores with a diameter of more than 50 m.

Example 4: Preparation of a Tubular Sputtering Target Containing an Indium-Tin Coating

Providing an Indium-Tin Coating on a Carrier Tube

[0140] An indium-tin alloy (90 wt % In, 10 wt % Sn) was melted in a crucible. Following the procedure as described in Example 1, an indium-tin coating was provided on the carrier tube by spraying. A non-segmented indium-tin coating was obtained (i.e. no seams in circumferential direction). The density of the metal coating was about 80% of the theoretical density. The metal coating had a porosity of about 20%.

Densifying the Metal Coating by Applying a Contact Pressure with a Densification Tool

[0141] Following the procedure as described in Example 1, the sprayed indium-tin coating was subjected to a densification treatment by rolling.

[0142] In the beginning of the densification step, a contact pressure of about 3.5 MPa was applied by each of the rolls to the metal coating. For making sure that the metal coating is still plastically deformed while its density is increasing, the contact pressure applied by the rolls was increased during step (c) to a maximum value of 8 MPa.

[0143] After 10 repetitions of the spiral path of the densification tools over the metal coating, a densified metal coating having a porosity of 5% was obtained. The density of the metal coating was 95% of its theoretical density. The densified metal coating did not contain pores with a diameter of more than 50 m.

Comparative Example 1: Preparation of a Tubular Sputtering Target Containing an Indium Coating, No Treatment with a Densification Tool

[0144] Highly pure indium (99.999%) was melted in a crucible. A carrier tube provided with a rough adhesion-promoting layer was mounted on a rotary device. The melted indium metal, i.e. the liquid metal phase, was supplied by a feed line to an atomizer nozzle where it was sprayed by the action of a gas. The liquid drops hit the rotating carrier tube and solidify, and a relative motion of the carrier tube versus the spray nozzle caused a metallic indium layer, i.e. the metal coating, to be deposited in the form of multiple layers on the carrier tube over time. A non-segmented metal coating was obtained (i.e. no gap in circumferential direction). The density of the metal coating was about 80% of the theoretical density. The metal coating had a porosity of about 20%.

Comparative Example 2: Preparation of a Tubular Sputtering Target Containing an Indium Coating, Densification Treatment by Isostatic Pressing

Providing an Indium Coating on a Carrier Tube

[0145] Highly pure indium (99.999%) was melted in a crucible. A carrier tube provided with a rough adhesion-promoting layer was mounted on a rotary device. The melted indium metal, i.e. the liquid metal phase, was supplied by a feed line to an atomizer nozzle where it was sprayed by the action of a gas. The liquid drops hit the rotating carrier tube and solidify, and a relative motion of the carrier tube versus the spray nozzle caused a thick metallic indium layer, i.e. the metal coating, to be deposited in the form of multiple layers on the carrier tube over time. A non-segmented metal coating was obtained (i.e. no gap in circumferential direction). The density of the metal coating was about 80% of the theoretical density. The metal coating had a porosity of about 20%.

Densifying the Metal Coating by Applying a Contact Pressure Via Cold-Isostatic Pressing (CIP)

[0146] The indium-coated carrier tube was water-tightly put into a CIP mould made of silicone. Pressing was carried out at 500 bar in water.

[0147] The density of the metal coating was about 96% of the theoretical density. The metal coating had a porosity of about 4%. However, a so-called elephant foot was formed which had to be removed by over-twisting, thereby resulting in an undesired loss of material.

[0148] If compared to the densification treatment by using rolls (Inventive Examples), a significantly longer process time and higher energy input were needed for reducing porosity of the sprayed indium coating to a final porosity value of about 4%.

III. Sputtering Tests Using the Sputtering Targets of Example 1 and Comparative Examples 1-2

[0149] Using the sputtering targets of Example 1 and Comparative Examples 1-2, indium layers were sputtered onto glass substrates.

[0150] For each of these sputtering targets, the maximum power input achievable during the sputtering process was determined. Furthermore, quality of the sputtered indium film (in terms of homogeneity) was evaluated qualitatively.

[0151] The maximum power input achievable during the sputtering process was determined as follows:

[0152] Starting from 10 kW/m, the power input to a sputtering target having a length of 500 mm was increased step-wise by 0.25 kW per step. At each step, the power input level was maintained constant for one hour. If the critical limit of the power input is passed, the sputtering material (i.e. the indium coating) starts to melt, and there is a sudden increase of the arcing rate by several orders of magnitude. The power input being applied to the sputtering target just before passing the critical limit represents the maximum power input achievable during the sputtering process.

[0153] The results of the sputtering tests are summarized in Table 1.

TABLE-US-00002 TABLE 1 Properties of the metal coating (i.e. the sputtering material) and results of the sputtering tests Sputtering Sputtering Sputtering target of target of target of Comparative Comparative Example 1 Example 1 Example 2 Porosity 4% 20% 4% Relative Density 96% 80% 96% Pores with diameter of No Yes No at least 50 m Time needed for Short Short Very long preparing the sputtering target Energy input needed Low Low Very high for the densification treatment Critical power limit 22 kW/m 15 kW/m 22 kW/m during sputtering Arcing (at 10 kW/m) Low High Low Homogeneity of the High Low High sputtered indium layers

[0154] As demonstrated by the examples, the process of the present invention provides non-segmented sputtering targets of sufficient length for large-scale sputtering applications at low process times and low energy input. Furthermore, the sputtering targets obtained from the process of the present invention can be operated at a high power input with low arcing and provides a sputtered product of high homogeneity.