High-strength steel^[1]

Yield strength > 1370MPa

Tensile strength>1620MPa

EX:Maraging steel

WC cemented carbide/tungsten carbide

Tungsten carbide (WC) and binder cobalt (Co)

Tungsten carbide, titanium carbide (TiC) and cobalt

Tungsten carbide, titanium carbide, tantalum carbide (or niobium carbide) and cobal

Sintered tungsten alloy

Generally speaking, after tungsten powder is formed, the dense body obtained through sintering is a kind of polycrystalline material, whose microstructure is composed of crystal. The sintering process directly affects grain size, pore size, grain boundary shape and distribution in the microstructure.

Well processed high density tungsten alloy

Deformation processes

Heat treatment

High density tungsten alloy composite

Tungsten alloys are alloys based on tungsten with other elements added.

EX:W-Ni-Fe、W-Ni-Cu、W-Ni-Cu-Fe 

In 1976, US army peripheral science and technology center (FSTC) held a special meeting and published the research results of the deformation-machined high-density tungsten alloy, indicating that the fourth-generation armor piercing tungsten alloy core material was basically developed. By the 1980s, a number of major countries in the world were equipped with tungsten alloy armor piercing shells on more than a dozen tanks and dozens of artillery pieces, with gun diameters ranging from 60mm to 125mm, and the maximum weight of the bullet core reaching 4kg, which were assembled in various forms (such as whole, multiple pieces and steel jackets). Due to the study and improvement of the mechanical properties and ballistic properties of high-density tungsten alloys, as well as the continuous improvement of the supply of tungsten raw materials, some people from the American society of heat-resistant metals have published articles arguing that tungsten should be used as the main material for armor piercing bullet cores.

Figure.1 Different type of armor piercing^[2]

• W-Ni-Fe

The sintering and heat treatment with two diameters were strengthened by means of thermal machining, which not only greatly improved the strength of the material, but also maintained a good elongation. Specific steps are: use stainless steel coating sealing the  billet in heating furnace in air to 100esulting in a final deformation of 97.5%. The ultimate microstructure of the material is mainly composed of elongated tungsten grains parallel to the axial direction. The existence of such microstructure is believed to be the reason for the substantial improvement of mechanical properties of the material.^[3][4]

                                                         Table.1 Different type of W-Ni-Fe^[5]

Microstructure

                                           [6]

• W-Ni-Cu

The tensile properties and hardness of WNF alloy at room temperature are superior due to the presence of finer W-grain size, lesser contiguity, and porosity in its microstructure. WNF alloy fails under tension by W-grain cleavage fracture due to relatively stronger matrix phase and W/matrix bonding. The tensile properties and hardness of WNC alloys at room temperature are inferior due to the presence of coarse W-grain size, higher contiguity, and porosity in their microstructure. WNC alloys fail under tension by matrix/interface fracture due to relatively weaker matrix phase and W/matrix bonding^[6].

Table.2. Different type of W-Ni-Cu^[7]

Fig.3 W ,Ni ,Fe and Cu elemental maps for (a) WNF, (b) WNC1 and (c)WNC2 alloy respectively^[8]

Fracture Properties^[7]

The deformation energy will increase with the hence of the density, which benefits the deformation and the breakage of the fragile of the armor-piercing projectile.

For the projectile of the same volume size, the mass of the projectile increases with the increasing density of the projectile body, which can not only improve the flight stability of the projectile body but also improve the ability to penetrate and damage the target. Among them, the material density is better in the range of 15 ~ 19 g· cm-3. The penetration process of a high-density brittle tungsten alloy projectile with a density of 15 g· cm-3, 17 g· cm-3 and 19 g· cm-3 to a target with a thickness of 10 mm is simulated. by lambda = 5, where the projectile body velocity is 1200 m/s and its tensile strength is 200 MPa. FIG. 1 shows the situation of projectiles of different densities penetrating the target plate at the moment and after penetrating the target plate. As can be seen in figure 1, with the increase of material density of the projectile body, the crushing effect of the projectile body after penetrating is improved correspondingly. Specifically, when the projectile penetrates the finite-thickness target, with the increase of material density of the projectile body, the projectile body flies farther, and the fragmentation phenomenon of the projectile body is more violent. For fragile penetrator projectile, the deformation of the projectile body during penetration will lead to deformation and failure of projectile body material. It can be seen that a higher density will enable the projectile to have larger deformation energy, which is conducive to the deformation and fragmentation of the fragile armor-piercing projectile.

Figure.1 Effect of material with different density ^[7]            Figure.2 Effect of material with different tensile strength^[7]

Tensile Strength^[7]

The projectile body length to diameter ratio λ = 5, which simulates the penetration process of a projectile body with tensile strength of 800 MPa, 500 MPa, and 200 MPa to a target with a thickness of 10 mm, in which the projectile body has a target velocity of 1200 m/s and a density of 19 g· cm-3. See fig.2 for the moment when the projectile penetrates the target plate and the situation after the projectile penetrates the target plate with various tensile strength. It can be seen from figure 2 that after penetrating the finite-thickness target, the crushing effect of the projectile body increases with the decrease of the material's tensile strength. Specifically, for projectile bodies with different tensile strength, there was no obvious tensile fracture in the process of penetrating the finite thickness target, and the overall structure was relatively complete. The penetrating ability of projectile bodies to the finite thickness target was not affected by the change of the material's tensile strength. After penetrating the finite-thickness target, with the decrease of the tensile strength of the material, a more violent crushing phenomenon occurs on the whole projectile body, and the remaining unbroken volume of the projectile body decreases correspondingly. Figure 3 shows that with the decrease of the tensile strength of the projectile body material, the projectile body has a better crushing effect after penetrating the target with limited thickness, which is manifested as a more violent crushing and deformation phenomenon of the projectile body. In the process of penetrating a finite-thickness target, due to the main compressive stress of the projectile body and the small influence of the tensile strength of the material, the deformation energy of projectile body with different tensile strength in the process of penetrating the target body does not differ much, and the tensile stress of projectile body in the process of penetrating the target plate is also close. Under the action of similar instantaneous tensile stress, the smaller the dynamic tensile strength of the projectile material is, the more easily the material is destroyed by stretching, and the more obvious the fragmentation phenomenon of the projectile body is. Therefore, the smaller the tensile strength of the projectile body material, the better the crushing effect of the projectile body after penetrating the target plate.

When the interface bonding between binder phase and W grain was higher, Relatively higher strength, toughness and elongation values( 883MPa, 29J and 10%) were observed. Strong strength causes the ductile fracture of the matrix and cleavage of w grains. The cleanliness of the W powder, matrix composition and the W-grain size would affect the strength of the interface between the W grain and the matrix.  Proper post-sintering heat treatment, however, avoids segregation of impurities at the tungsten–matrix interface and allows the impurities to remain homogeneously distributed throughout the matrix. Therefore, the post-sintering heat treatment causes great improvement in mechanical properties of WHAs^[8].

            Figure.5 Tensile fracture surfaces of (a)sintered, (b)sintered and heat treated^[9]

For example, tungsten alloys of the type described in U.S. Pat. No. 3,979,234 are suitable for use in the projectile of this invention. A suitable. composition for such an alloy is, for example, 93 wt.% tungsten, 4.55 wt.% nickel, 2.45 wt.% iron.

Figure.7 Armor piercing projectile(APCR)^[10]                                                                           Figure.8 Armor piercing projectile(APFSDS)^[11]

Processing Information

Manufacturing Information

[1]Baosheng, Z., &  Zhijun, K. (1999). Tunnel-piercing properties and applications of high-density tungsten alloys. China tungsten industry (z1), 178-181

[2]Mingxing, Z., & Xiaoxia, H. (2015). Study and analysis of tungsten alloy armor piercing core material strengthening technology and material technology abroad. Journal of weapons and equipment engineering, 36(12), 114-117.

[3]Fuyao,. W, Xingwang,. C & Hongnian,. C.(2007). Research on new tungsten alloy materials for armor-piercing projectile. Weapon materials science and engineering, 30(1), 46-48.

[4]Chengshang,. Z (2009). Study of the w-ni-fe high-density alloy by microwave sintering. (Doctoral dissertation, central south university).

[5]Haibin,. H, Yuhua,. C, Xiaoyan,.Z & Yubin, Z (2016). Cold rolling deformation behavior and microstructure characteristics of w-ni-fe high-density alloy sheet. Rare metals, 31(04).

[6]Das, J., Rao, G. A., & Pabi, S. K. (2010). Microstructure and mechanical properties of tungsten heavy alloys. Materials Science and Engineering: A, 527(29-30), 7841-7847.

[7]Shenghao, . Z& Peihui,.S. (2016). Research on the properties of fragile armor-piercing projectile materials. Journal of weapons and equipment engineering, 37(7), 144-148.

[8]R.M. German, L.L. Bourguignon, Powder Metall. Def. Technol. 6 (1984) 117–131.

[9]Das, J., Rao, G. A., & Pabi, S. K. (2010). Microstructure and mechanical properties of tungsten heavy alloys. Materials Science and Engineering: A, 527(29-30), 7841-7847.

[10]Ladislas, Permutter. "Armor piercing projectile." U.S. Patent No. 3,370,535. 27 Feb. 1968

[11]Davis, Dale M. "Armor piercing projectile." U.S. Patent No. 4,108,073. 22 Aug. 1978.