PREPARATION METHOD AND APPLICATION OF OXIDIZED CERAMIC LAYER ON SURFACE OF ZIRCONIUM AND ZIRCONIUM ALLOY

Abstract

The invention discloses a preparation method and application of an oxidized ceramic layer on the surface of zirconium and zirconium alloy. The method comprises the following steps: reducing the roughness of a target area to 0.01 μm or less, performing oxidation treatment in an oxidizing gas atmosphere, and replacing the oxidizing gas with inactive gas. According to the technical solution provided in the present application, the surface roughness is controlled before oxidation treatment, so that the surface roughness after oxidation treatment can satisfy the use requirements; and the inert gas replacement after surface oxidation treatment avoids the removal of a film layer with poor performance formed during the cooling process, thereby completely avoiding the need for later polishing treatment, maintaining the integrity and uniformity of the oxidized ceramic layer, and guaranteeing the protective performance.

Claims

1. A method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy, comprising steps of: 1) lowering a roughness of a targeted area of the zirconium or zirconium alloy on which a surface oxidization treatment is to be performed, the roughness being controlled to 0.01 μm or less; 2) performing the surface oxidation treatment in an atmosphere containing an oxidizing gas to form an oxidation ceramic surface layer; and 3) introducing an inactive gas to replace the oxidizing gas used in step 2) and initiating a cooling process to complete preparation of the oxidation ceramic surface layer without performing a subsequent treatment of lowering a roughness of the oxidation ceramic surface layer.

2. The method of claim 1, wherein the roughness is lowered to a value in the range of 0.002 μm to 0.010 μm in step 1).

3. The method of claim 1, wherein after the oxidation treatment in step 2), a thickness of the oxidation ceramic surface layer on the targeted area is controlled within a range of 1 μm to 20 μm.

4. The method of claim 1, wherein the surface oxidation treatment in step 2) comprises heating to a temperature in the range of 500° C. to 700° C. and maintaining the temperature for 0.5-10 h.

5. The method of claim 1, wherein the roughness of the targeted area is lowered in step 1) by means of grinding, mechanical polishing, fine machining, vibratory polishing or any combination thereof.

6. The method of claim 1, wherein the inactive gas in step 3) is one or more selected from the group consisting of nitrogen and rare gases.

7. The method of claim 1, wherein the targeted area for the surface oxidization treatment is an area to be brought into direct contact with another bearing surface.

8. The method of claim 1, wherein the atmosphere containing the oxidizing gas in step 2) is an atmosphere containing oxygen and/or ozone.

9. A method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy, comprising steps of: 1) lowering a roughness of a targeted area of the zirconium or zirconium alloy on which a surface oxidization treatment is to be performed, the roughness being controlled to 0.01 μm or less; 2) performing the surface oxidization treatment on the surface of the zirconium or zirconium alloy to form an oxidation ceramic surface layer; and 3) lowering a roughness of the formed oxidation ceramic surface layer.

10. A material for use in medical implants, comprising a metal substrate, an oxygen-rich diffusion layer and an oxidation ceramic surface layer, the metal substrate being made of zirconium or a zirconium alloy, wherein the oxygen-rich diffusion layer and the oxidation ceramic surface layer are formed by the method of claim 1. to 9.

11. The material of claim 10, wherein the medical implants are bearing implants used in a hip joint or knee joint.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic cross-sectional view illustrating the structure of a material for use in medical implants according to particular embodiments.

[0028] FIG. 2 is a metallurgical microscope image showing cross section of Sample 1 that has been oxidized according to Embodiment 1.

[0029] FIG. 3 is a metallurgical microscope image showing cross section of the sample of FIG. 2 that has been ground and polished.

[0030] FIG. 4 is a metallurgical microscope image showing cross section of Sample 2 that has been oxidized according to Embodiment 1.

[0031] FIG. 5 is a metallurgical microscope image showing cross section of Sample 3 that has been oxidized according to Embodiment 2.

[0032] FIG. 6 is a metallurgical microscope image showing cross section of the sample of FIG. 5 that has been ground and polished.

[0033] FIG. 7 is a metallurgical microscope image showing cross section of Sample 4 that has been oxidized according to Embodiment 2.

[0034] FIG. 8 is a metallurgical microscope image showing cross section of Sample 5 that has been oxidized according to Embodiment 3.

[0035] FIG. 9 is a metallurgical microscope image showing cross section of Sample 6 that has been oxidized according to Embodiment 3.

[0036] In the figures,

[0037] 10, oxidation ceramic surface layer; 20, oxygen-rich diffusion layer; 30, metal substrate.

DETAILED DESCRIPTION

[0038] The method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy comprises the following specific steps:

[0039] (1) Lowering roughness Ra of the zirconium/zirconium alloy surface on which the surface oxidization treatment is to be performed, at least the portion thereof to be brought into direct contact with another bearing surface to a value below 0.01 μm (i.e., Ra<0.01 μm), preferably in the range of 0.002-0.010 μm (i.e., Ra=0.002-0.010 μm), more preferably in the range of 0.003-0.008 μm (i.e., Ra=0.003-0.008 μm). For example, Ra may be lowered into the range of 0.004-0.007 μm (i.e., Ra=0.004-0.007 μm) or of 0.005-0.006 μm (i.e., Ra=0.005-0.006 μm). Here, the word “bearing” means the relationship that the surface of the implant is to be squeezed against and moves relative to another object (another implant or human bone, etc.), such as the relationship between the tibial joint surface of knee joint and the femoral joint surface. The term of “another bearing surface” refers to the surface of another implant or human bone to be brought into contact with the implant surface that has been performed a surface oxidization treatment.

[0040] The common zirconium or zirconium alloy medical implants that have been performed surface oxidization treatments, in particular hip or knee joint prostheses fabricated from zirconium-niobium alloys, are generally required to have a surface roughness of 0.02 μm or less. Such surface roughness has to be realized by polishing the oxidation ceramic surface layer after oxidation treatment in prior art. On the contrary, according to present application, the metal surface is pre-treated to control the roughness within a predetermined range in advance. Inventors have confirmed through repeat experiments that the metal having the roughness within the predetermined range is able to be oxidized and thus form an oxidation ceramic surface layer having a surface roughness that meets application requirements directly, enabling to omit the polishing step after the oxidization treatment. In this surface roughness control step, if the roughness Ra is lowered to a value above 0.010 μm, the oxidation ceramic layer resulting from the surface oxidation treatment may have a surface roughness Ra greater than 0.02 μm that fails to satisfy requirements; and if the roughness Ra is lowered to 0.002 μm or less, the cost is too high and the roughness exceed actual needs, which is thus not recommended in consideration of cost effectiveness

[0041] The surface roughness modification can be accomplished by grinding, mechanical polishing, fine machining, vibratory polishing or any combination thereof.

[0042] (2) Performing a surface oxidation treatment to the zirconium or zirconium alloy that has the surface roughness thereof changed in step (1). Specifically, the zirconium or zirconium alloy from step (1) is placed in an atmosphere containing an oxidizing gas, heated to a temperature in the range of 500-700° C. (Preferably, 550-600° C.) and maintained the zirconium or zirconium alloy at the high temperature for 0.5-10 h (Preferably, 2-6 h). The oxidation ceramic surface layer formed on the zirconium or zirconium alloy has a thickness of 1-20 μm, preferably 3-10 μm, more preferably 3-7 μm, e.g., 4 μm, 5 μm or 6 μm. The oxidizing gas refers to the gas having an oxidizability, such as oxygen or ozone, and the atmosphere containing the oxidizing gas refers to the atmosphere that contains said oxidizing gas and is preferred to be air in consideration of economy and easy availability.

[0043] If the oxidation ceramic surface layer grows to have an excessively large thickness, the occurrence of numerous micro-cracks in the layerc as well as the poor bonding strength and bad wear resistance are resulted. If the layer is too thin, it may suffer from insufficient wear resistance. If the oxidation ceramic surface layer has a thickness in the above range, the layer is able to have an optimal internal compactness, a high bonding strength and an excellent wear resistance. The surface oxidation ceramic layer does not need to be too thick as there is no need to polish the layer in subsequent. Therefore, the thickness of surface oxidation ceramic layer can be controlled within the above range directly and the elimination of subsequent polishing enables to prove integrity and uniformity of the oxidation ceramic surface layer, resulting in additional improvements in its overall performance.

[0044] Preferably, during a cooling process, the oxidizing gas may be replaced by introducing nitrogen or an inert gas such as helium, neon or argon, or any combination thereof. In this way, surface oxidation treatment of the zirconium/zirconium alloy is terminated and the temperature slowly declines to room temperature.

[0045] The subsequent replacement with the inactive gas avoids the formation during the cooling process of a membrane layercoating with inferior quality that has to be removed in subsequent, thus resulting in a further increase in the quality of the oxidation ceramic surface layer. Through the upstream roughness control and the downstream gas replacement, the polishing after oxidization treatment is successfully omitted and thus the problems arising from the polishing are solved.

[0046] The above method can be used to fabricate a material for use in medical implants, which includes a metal substrate 30, a oxygen-rich diffusion layer 20 and a oxidation ceramic surface layer 10 that are arranged from inside to outside, as shown in FIG. 1. The metal substrate 30 is a metallic material that has not experienced a surface oxidation treatment. The oxidation ceramic layer 10 is a layer in which oxygen element is present essentially in the form of the oxide. The oxygen-rich diffusion layer 20 is a layer in which the content of oxygen is higher than the content of oxygen in metal substrate and the oxygen element is present essentially in the form of solute atoms. Here, the metal substrate 30 is zirconium metal or a zirconium alloy, and the oxygen-rich diffusion layer 20 and the oxidation ceramic surface layer 10 are formed by the above method. Such material is suitable for use in the fabrication of medical implants, in particular bearing implants in hip or knee joints, which are required to have bearing performances.

[0047] It is to be noted that in each of the metallurgical microscope photographs shown in FIGS. 2 to 9, the middle dark region is an oxidation ceramic surface layer 10, and the rightmost brightest region is a metal substrate 30. Limited by the ability of the used metallurgical microscope, it would be difficult to distinguish an oxygen-rich diffusion layer 20 from a metal substrate 30 in the photos. In fact, the oxygen-rich diffusion layer 20 is a light-colored layer having a thickness of 1 to 2 μm and close to the dark-colored oxidation ceramic surface layer 10.

[0048] For ease of understanding, the method for preparing an oxidation ceramic layer on a surface of zirconium or a zirconium alloy will be further described below with reference to several embodiments. These embodiments are presented for the mere purpose of illustrating the present application and do not limit protection scope thereof in any sense.

[0049] Unless particularly noted, each material or reagent used in the following embodiments is commercially available, and each process or parameter adopted in the method can be realized by conventional techniques.

Embodiment 1

[0050] Zr-2.5 Nb alloy (a zirconium alloy containing 2.5 wt % of Nb) samples were ground and polished so that Sample 1 had a lowered surface roughness Ra of 0.3792 μm and Sample 2 had a lowered surface roughness Ra of 0.0038 μm. The samples 1 and 2 were together placed into a tube furnace, heated to 550° C. in air and maintained at the temperature for 6 h. Subsequently, air was evacuated and argon was introduced to the furnace. After the slow cooling at a rate of 5° C./min to 100° C. or below, the samples 1 and 2 were taken out and measured with a roughness gauge. The results showed, after the oxidation treatment, the roughness Ra of Sample 1 increased to 0.6852 μm and that of Sample 2 increased to 0.0158 μm. FIG. 2 is a metallurgical microscopic image of a cross section of Sample 1 that has been oxidized, which shows a metal substrate (right), an oxidation ceramic surface layer (left) and an oxygen-rich diffusion layer between the metal substrate and the oxidation ceramic surface layer. At this time, a cross section image of Sample 1 after the oxidation treatment was taken and shown in FIG. 3. Since the surface roughness Ra of Sample 2 after the oxidation treatment has already met the requirement of Ra<0.02 μm, there is no need to perform a polishing treatment. The cross section image of Sample 2 after the oxidation treatment was taken by a metallurgical microscope and shown in FIG. 4.

[0051] As can be seen from FIG. 2, Sample 1 that has experienced surface oxidation treatment possesses an oxidation ceramic surface layer having an average thickness of about 5.82 μm. Such thickness falls in the optimal thickness range of 3-7 μm. However, as the surface of sample 1 before oxidation treatment fluctuates seriously, the interface between the oxidation ceramic surface layer and the substrate fluctuates seriously. In addition, the growth of the oxidation ceramic surface layer was accompanied by the increase of surface roughness. The above two factors together results in the sharp increase of surface roughness of the oxidation ceramic surface layer. FIG. 3 is a metallurgical microscope image showing the cross section of Sample 1 that has been further ground and polished to a Ra of 0.0184 μm. As can be seen, after being ground and polished, the remaining oxidation ceramic surface layer exhibits an extremely uneven distribution of thickness, even the exposure of zirconium-niobium alloy substrate at partial area. The reason for this was that during the grinding and polishing process for a low roughness, the convex portions of the oxidation ceramic surface layer experiences a large thickness loss while the concave portions thereof experiences few thickness loss. After the grinding and polishing treatment, the oxidation ceramic surface layer has a thickness of 4.728 μm at the thickest location but almost no reservation of the oxidation ceramic layer at the thinnest location. Apparently, this oxidation ceramic surface layer is unusable.

[0052] By contrast, Sample 2 of FIG. 4 had an oxidation ceramic surface layer with a thickness of about 6.21 μm within the optimal thickness range of 3-7 μm. Since the initial surface roughness of Sample 2 is very low, the formed oxidation ceramic surface layer has a uniform thickness varying from 5.859 μm to 6.373 μm, i.e., having a tolerance of only 0.26 μm. Since this oxidation ceramic surface layer was totally satisfactory in terms of surface roughness, it is unnecessary to perform a further polishing treatment and integrity of the layer would not be impaired, so that the oxidation ceramic surface layer is able to possess a great improvement in property. The oxidation ceramic surface layer obtained by the present method has a uniform thickness, in which the interface between the surface oxidation ceramic layer and the substrate is substantially a horizontal plane, making it an ideal oxidation ceramic surface layer of a zirconium/zirconium alloy.

Embodiment 2

[0053] Industrial pure zirconium were ground and polished so that Sample 3 had a lowered surface roughness Ra of 0.3886 μm and Sample 4 had a lowered surface roughness Ra of 0.0042 μm. Samples 3 and 4 were together placed into a tube furnace, heated to 600° C. in air and maintained at the temperature for 4 h. Subsequently, air was evacuated and argon was introduced to the furnace. After the slow cooling at a rate of 5° C./min to 100° C. or below, the samples 3 and 4 were taken out and measured with a roughness gauge. The results showed, after the oxidation treatment, the roughness Ra of Sample 3 increased to 0.7705 μm and that of Sample 4 increased to 0.0158 μm. FIG. 5 is a metallurgical microscopic image showing a cross section of Sample 3 that has been oxidized, while FIG. 6 is a metallurgical microscopic image showing a cross section of Sample 3 that has been further ground and polished to a surface roughness Ra of 0.0177 μm. Since the surface roughness Ra of Sample 4 after the oxidation treatment has already met the requirement of Ra<0.02 μm, there is no need to perform a polishing treatment. The cross section image of Sample 4 after the oxidation treatment was taken by a metallurgical microscope and shown in FIG. 4.

[0054] As shown in FIG. 5, Sample 3 that has experienced surface oxidation treatment possesses an oxidation ceramic surface layer having an average thickness of about 8.66 μm. The surface of Sample 3 fluctuates seriously and the interface between the oxidation ceramic surface layer and substrate in Sample 3 is a curved interface. FIG. 6 is a metallurgical microscope image showing the cross section of Sample 3 that has been further ground and polished to a Ra of 0.0177 μm. After the grinding and polishing treatment, the oxidation ceramic surface layer remains a thickness of 5.037 μm at the thickest location and a thickness of merely 1.439 μm at the thinnest location. Although the ground and polished oxidation ceramic surface layer still covers the entire surface of Sample No. 3, the remaining oxidation ceramic surface layer has an uneven thickness and a poor protective performance at relatively thin locations. Notably, in order to ensure total coverage of the oxidation ceramic surface layer after the grinding and polishing treatment, the surface oxidation treatment is required to prepare a thicker oxidation ceramic surface layer. However, the oxidation ceramic surface layer formed under the above roughness has already exceeded the optimal thickness range of 3-7 μm, which affects the performance of the surface oxidation ceramic layer.

[0055] As shown in FIG. 7, after the oxidation treatment, Sample 4 had an oxidation ceramic surface layer with an average thickness of about 10.22 μm. While the thickness is out of the optimal range (3-7 μm), the sample surface remains to be flat. The oxidation ceramic surface layer is uniform in thickness and had a flat, clear interface with the substrate as well as good protective properties.

Embodiment 3

[0056] Zr-2.5 Nb alloy samples were ground and polished so that Sample 5 had a lowered surface roughness Ra of 0.0056 μm and Sample No. 6 had a lowered surface roughness Ra of 0.0055 μm. Samples 5 and 6 were placed into separate tube furnaces, and were both heated to 600° C. in air and maintained at the temperature for 4 h. Subsequently, for the furnace with Sample 5 placed therein, air was evacuated from and argon was introduced to the furnace following by the slow cooling at a rate of 5° C./min to 100° C. or below. Then, Sample 5 was taken out from the furnace. By contrast, Sample 6 was slowly cooled still in the oxidizing atmosphere at a rate of 5° C./min to 100° C. or below and then taken out. As measured with a roughness gauge, after the oxidation treatment, the roughness Ra of Sample 5 increased to 0.0162 μm and that of Sample 6 increased to 0.0426 μm.

[0057] FIG. 8 is a metallurgical microscope image showing the cross section of Sample 5. FIG. 8 shows that the formed oxidation ceramic layer has a uniform average thickness of about 9.54 μm and a flat surface as well as a flat and straight interface with the substrate. Since the roughness Ra is within the range of Ra<0.02 μm, Sample 5 can be directly used in the fabrication of a bearing implant such as a hip or knee joints without further polishing. As Sample 6 is cooled in the initial oxidizing atmosphere, the surface of Sample 6 continues to be oxidized in the cooling process, so as to form a thicker oxidation ceramic surface layer. As shown in FIG. 9, the formed oxidation ceramic surface layer has a thickness of about 11.28 μm, and poor-quality oxides are present on the outer surface of the layer, which remarkably raises the surface roughness of Sample 6 that has been oxidized beyond the range of Ra<0.02 μm. Therefore, it has to be further polished before it can meet the application requirements of bearing implants such as hip and knee joints. Nonetheless, thanks to the polishing treatment prior to the oxidation treatment, the oxidation ceramic surface layer has a flat interface with the substrate, which allows the layer to maintain a uniform thickness after polishing and eliminate the problems of non-uniform thickness and excessive low thickness at some locations.

[0058] In summary, according to present application, roughness Ra of a zirconium/zirconium alloy surface has been lowered to Ra<0.01 μm before the surface oxidization treatment, allowing the oxidation ceramic surface layer to grows to the optimal thickness as well as enabling to control the roughness just within the required range (Ra<0.02 μm) of finished product. The cooling process in an inert atmosphere enables to avoid performance degradation of the oxidation ceramic surface layer during the cooling process, thereby enabling the grounding and polishing treatment after the oxidation treatment to be omitted to obtain an integral oxidation ceramic surface layer. In addition, as it is unnecessary to reserve a certain thickness for the loss arising from the grinding and polishing treatment, the oxidation ceramic surface layer is allowed to grow exactly to the optical thickness. This enables the oxide layer to have an optimal internal compactness, a high bonding strength and an excellent wear resistance.

[0059] It is to be noted that, the medical implants as mentioned herein refer to implantable medical instruments that can be placed into surgically created or naturally occurring cavities in human bodies. Examples of the medical implants may include, but are not limited to, surgical implants such as artificial joints, (orthopedic, spinal, cardiovascular and neurosurgical) implants, structural prostheses, dentures and other artificial organs; implants made of metal materials (including stainless steel, cobalt-based alloys, titanium and alloys thereof and shape memory alloys), polymers, high molecular materials, inorganic non-metallic materials, ceramic materials, etc.; implantable instruments such as implantable orthopedic instruments, implantable aesthetic and plastic surgical instrument and materials; implantable appliances such as bones (plates, screws, pins, rods), intra-spinal fixation devices, staplers, patellar concentrators, bone wax, bone repair materials, plastic surgical materials, heart or tissue repair materials, intraocular filling materials, nerve patch, etc.; interventional instruments such as interventional catheters, stents, embolization and other devices; and orthopedic (orthopedic) surgical instruments such as scalpels, drills, scissors, forceps, saws, chisels, files, hooks, needle slickers, active instruments, extremity extension braces, multi-purpose unilateral external fixation devices and other instruments for orthopedic (orthopedic) surgical use.

[0060] Finally, it is to be noted that the above embodiments are provided merely to illustrate the technical solution of present application and are not intended to limit it in any way. Although the present application has been described in detail with reference to the above embodiments, modifications to those embodiments are still possible, or equivalent substituents of all or some of the technical features thereof can be made by those of ordinary skill in the art. Such modifications substituents do not cause the essence of corresponding technical solution to depart from the protection scope of the various embodiments of the present application.