1. Introduction to the properties of titanium and titanium alloys

 

Introduction to titanium: Titanium is a new type of material with the advantages of low density, high specific strength, heat resistance and corrosion resistance. It weighs only half of iron, but its mechanical properties such as hammering and drawing are comparable to those of copper. Generally speaking, as the temperature decreases, the impact resistance of metals will decrease, but titanium is just the opposite. The lower the temperature, the harder titanium will become, and superconductivity will occur when the critical temperature is reached.

 

Introduction to titanium alloys:

Titanium alloys and titanium are similar in nature to a certain extent, with the characteristics of low density and high strength. In addition, their mechanical properties are very excellent and their corrosion resistance is strong. Moreover, their thermal strength is high, which is significantly better than that of aluminum alloys. At the same time, their mechanical properties do not change much at low and ultra-low temperatures.

 

2. New processes, new technologies and new uses of titanium

 

2.1 Preparation methods of titanium

 

Although titanium is relatively abundant in nature, it is also a rare metal because it is dispersed and difficult to extract. At present, the preparation of titanium is divided into two categories: thermal reduction method and molten salt electrolysis method.

 

(1) Preparation of titanium by thermal reduction method

The thermal reduction method is to reduce titanium from titanium compounds such as TiCl 4 , TiO 2 , K 2 TiF 6 , etc. at a certain temperature using strong reducing agents such as Li, Na, Mg, Ca and their hydrides. According to the different titanium compounds, the thermal reduction method for preparing titanium can be divided into three categories:

 

① Redox method of titanium chloride, such as Kroll method, Hunter method, Armstrong method and EMR method;

 

② Redox method of titanium oxide, such as OS method, PRP process, MHR method;

 

③ Redox method of titanate.

 

Currently, only Kroll method and Hunter method can be successfully applied in industrial production. Kroll method uses magnesium metal to replace titanium in chloride, and Hunter method uses sodium metal to replace titanium in chloride. In addition, the Armstrong method developed by Chicago International Titanium Powder Company in the United States has a preparation method similar to Hunter method, which also uses reducing agent sodium to purify titanium metal. The United States has begun to use this method for pre-production in factories.

 

(2) Preparation of titanium by molten salt electrolysis

In 1959, Kroll predicted that molten salt electrolysis would replace the Kroll method and become the mainstream method for producing titanium in the next 5-10 years. Over the years, domestic and foreign research institutions and laboratories have developed a total of more than a dozen new technologies for preparing titanium by molten salt electrolysis. They can be divided into the following three categories according to the raw materials:

 

① Electrolysis of titanates;

 

② Electrolysis of titanium chlorides;

 

③ Electrolysis of titanium oxides, including FFC Cambridge method, MER process, USTB process, QIT process, SOM method and ionic liquid electrolysis.

 

New uses of titanium

Since the 1940s, the use of titanium has developed rapidly and has been widely used in aircraft, rockets, missiles, artificial satellites, spacecraft, ships, military industry, medical care and petrochemicals. The latest research has found that the human body contains a certain amount of titanium, which can stimulate phagocytes and enhance immunity. Therefore, many laboratories are committed to the development and application of bio-titanium.

 

3. New processes, technologies and new uses of titanium alloys

 

Preparation methods of titanium alloys

 

The traditional processing of titanium alloys generally adopts melting and casting technology. The latest processing technologies are divided into the following categories:

 

(1) Near-net forming technology;

 

(2) Wire friction welding technology;

 

(3) Superplastic forming technology;

 

(4) Computer simulation technology of material preparation and processing process.

 

Near-net forming technology includes laser forming, precision casting, precision die forging, powder metallurgy, injection molding and other methods. Powder metallurgy is a new process that uses titanium powder or titanium alloy powder as raw material, through forming and sintering, to manufacture titanium parts. The first step is to produce powder, generally using the mechanical alloying method, using a ball mill to strongly impact, grind and stir the raw materials. Then the alloy that has been formed into powder is pressed and formed. There are two pressing methods, namely pressure forming and pressureless forming. The purpose of this step is to obtain a certain shape and size of the pressed embryo, and to make it have a certain density and strength. Then, the blank is subjected to discharge plasma sintering. The upper and lower dies and the energized electrodes are used to apply a specific sintering power supply and pressing pressure to the sintered powder. After discharge activation, thermoplastic deformation and cooling, high-performance titanium materials are obtained. Then, the titanium alloy after plasma sintering is subjected to subsequent treatment, generally heat treatment or plastic processing.

 

New uses of titanium alloys

Titanium alloys were widely used in the aerospace field in the early days, mainly used to make aircraft engines or pneumatic components. Later, with the continuous development of technology, titanium alloys have entered the lives of ordinary people, and titanium alloys are also found in factories or household devices. Now countries and institutions are competing to develop new titanium alloys with low cost and high performance. In recent years, the new development of titanium alloys has mainly focused on the following five aspects.

 

(1) Medical titanium alloys

Titanium alloys have low density and good biocompatibility. They are ideal medical materials and can even be implanted in the human body. Titanium alloys used in the medical field before contain vanadium and aluminum, which can cause harm to the human body. However, recently, Japanese scholars have developed a new type of titanium alloy with good biocompatibility. However, this alloy has not yet been mass-produced. It is believed that in the near future, this type of high-quality alloy will be widely used in daily life.

 

(2) Flame-retardant titanium alloy

Titanium-based alloys that can resist combustion under certain pressure, temperature and air flow rate are flame-retardant titanium alloys. The United States, Russia and China have successively developed new flame-retardant titanium alloys. Among them, the United States uses these flame-retardant titanium alloys in engines. Because these titanium alloys are not sensitive to combustion, they can greatly improve the stability of the engine.

 

(3) High-strength and high-toughness β-type

β-type titanium alloys have the characteristics of high strength, good weldability, and excellent hot and cold processing performance. Using this law, the researchers prepared β-type titanium alloys with obvious characteristics: good hot processing performance, good plasticity, and good welding performance. And after solid solution-aging treatment, its mechanical properties are greatly improved. At present, Japan and Russia have prepared such titanium alloys.

 

(4) Titanium has many advantages that other metals cannot match. With the progress of society and the development of science and technology, the application of titanium and titanium alloys will become more extensive, and the demand for titanium and titanium alloys will increase day by day. However, the high production cost is one of the main reasons that restrict the promotion and use of titanium and titanium alloys. Therefore, the development and application of low-cost, large-scale and environmentally friendly continuous production processes can make titanium and titanium alloys more widely used.