CS249915B1 - Method of tia13 diffusion layer formation on titanium and its alloys - Google Patents

Abstract

The essence of the method of creating protective diffusion TiAk layers on titanium and titanium alloys, which increases corrosion resistance and abrasion at elevated temperatures lies in that an electrically conductive substrate is formed titanium or titanium alloys, which forms the cathode in the ion cladding system, is treated with an inert plasma gas and aluminum vapor reduced pressure from 10 ~ 2 to 102 Pa, behind it further titanium and titanium alloys with a blinker layer heats up in a thermal appliance protective atmosphere treatment to a temperature from 600 ° C to 655 ° C after for at least 1 hour.

Description

At present, TiAb layers are formed by diffusion of aluminum into titanium and its alloys, the aluminum layer being formed e.g. by galvanic methods or by mechanical cladding of aluminum foil and the like.

A disadvantage of the methods used hitherto is that they do not guarantee the desired surface cleanliness, which results in a deterioration in the diffusion of aluminum into titanium and its alloys and in the imperfect formation of a TiAb diffusion layer.

The above-mentioned drawbacks are solved by the method according to the invention, which is based on the electrically conductive substrate made of titanium or titanium alloy, which forms a cathode in the ion cladding system, with a plasma of inert gas and aluminum vapors under reduced pressure from 10 to ² 10 ² Pa, for the further substrate of titanium and titanium alloys with the aluminum layer is heated in the apparatus for heat treatment in a protective atmosphere to a temperature in the range 600 DEG C. to 655 DEG C. for at least 1 hour. The cathode is at a negative potential of 0 to 10 kV compared to the vacuum chamber. Due to the vacuum conditions and the continuous cleaning of the substrate surface in an inert gas discharge, during the deposition of the aluminum layer, suitable conditions are created for the subsequent diffusion of aluminum into the substrate during diffusion annealing outside the vacuum chamber.

By this method of the invention in the surface layer of titanium or its alloys, a layer consisting of TiAl3 and a solid solution of aluminum in titanium is formed.

The TiAb layer formed according to the invention on titanium or its alloys is perfectly adhering, with a microhardness of 14,000 to 16,000 N. . mm ^-2 , further reduces the coefficient of friction compared to titanium alloys by 400% and the wear measured by the method of weight loss by 800 ° / o. High temperature tests have shown that the TiAb layer is resistant to air oxidation at temperatures up to 900 ° C in the long term,

Examples of design

The process of forming the TiAb layer according to the invention takes place in two stages. In the first stage the formation of the Al layer on the substrate takes place, in the second stage the diffusion annealing of the substrate with the Al layer takes place outside the vacuum chamber in the protective atmosphere of the annealing furnace.

Since the diffusion of Al into titanium or its alloys is also dependent on the alloys which the substrate comprises, examples of embodiments of the invention are described in this regard. The first example shows the preparation of TiAb layer on the titanium alloy OT4-1, which is alloyed with Al and Mn and in the second example on the titanium alloy VT3-1, which is alloyed with Al, Mo, Cr and Si, where diffusion of Al compared to OT4 -1 is more difficult and therefore the annealing conditions must be different.

The selection can be explained by the following examples:

Example 1

Prior to the actual process of forming the Al layer 11a of the titanium alloy OT4-1, the vacuum chamber of the ion cladding device is pumped to a pressure of the order of 10 ^-3 Pa. Al is vaporized by means of an electron beam, which ensures a high growth rate of the Al layer and, compared to vaporization from a vaporized source, also a higher kinetic energy of vaporized Al particles. In this case, the evaporation of Al by means of an electron beam goes through so-called electron beam. cleaning as well as heating the substrate in an Ar discharge, which proceeds as follows: Ar is admitted to a pressure of 2 Pa through the inlet valve into the vacuum chamber. When this pressure is reached, a negative voltage of 2.5 kV over the grounded vacuum chamber is set in the next step on the substrate. By regulating the voltage on the substrate, the discharge conditions in the Ar are created at given parameters so that the surface of the substrate is degassed for 15 minutes, thin oxide films are removed from the surface and the substrate is heated to a temperature of at least 200 ° C. If the above conditions are met, then all the requirements for adhesion of the Al layer and its diffusion into the titanium alloy OT4-1 are met.

In the next step, Al is evaporated by means of an electron beam at a pressure of 1.10 ^-1 Pa and its power of at least 2 kW. The growth rate of the Al layer at a power of 2 kW and a substrate-evaporator distance of approximately 20 centimeters is about 2.0 μ ccaη. min ^-1 . During the evaporation of Al, the substrate surface continues to be continuously bombarded with ionized Ar particles. The thickness of the deposited Al layer depends on the desired depth of the resulting TiAb diffusion layer, with normally required thicknesses of about 10 μΐη. After the evaporation of Al and completion of cooling, the substrate is removed from the vacuum chamber.

In a further stage, the aluminum-treated OT4-1 titanium alloy substrate is diffusion annealed in a protective atmosphere (for example, in an Arj annealing furnace at 600 ° C for 1 hour. In this way, with respect to pretreatment of the substrate surface (Ar discharge cleaning) and large the growth rates of the Al layer on the cleaned and heated substrate surface are created conditions for diffuse Al into its surface and subsequent reaction between Ti and Al to form a hard abrasion-resistant and refractory TiAb layer.

Example 2

In the second example, TiAb layer preparation, TiAb layer formation conditions on the titanium alloy TV3-1 are shown. The process of cleaning the substrate surface in an Ar discharge and evaporating the Al layer is identical to the conditions set forth in Example 1. 1. The difference is in the VT3-1 substrate annealing mode outside the vacuum chamber, the annealing temperature being 655 ° C and the annealing time of at least 2 hours.

The above properties of the T1AI3 layers predetermine the use of articles of titanium or its alloys coated according to the invention, e.g. in Florida, marine waters and also construction joints in combination with aluminum without the danger of titanium weld at elevated operating temperatures. Titanium is highly susceptible to seizure and therefore its surface needs to be modified, especially if it is to be used for movement mechanisms, e.g. in the textile, engineering and chemical industries and the like.

Claims (1)

A process for forming a T1AI3 diffusion layer on titanium and its alloys, characterized in that a plasma of inert gas and aluminum vapor is depressurized to an electrically conductive substrate of titanium or titanium alloys which forms the cathode in the ion cladding system under reduced pressure from 10 ^-2 to 10 ² Pa, in the further substrate is made of titanium and titanium alloys, the aluminum layer is heated in a protective atmosphere to a temperature in the range 600 DEG C. to 655 DEG C. for at least 1 hour.