3D printed titanium components are favored in the aerospace, medical and automotive industries due to their high strength-to-weight ratio. Scientists from NUST MISIS have proposed a technology that can double the strength of composite materials obtained from aluminum powder through 3D printing, and improve the characteristics of these products to the quality of titanium alloys (the strength of titanium) It is about six times that of aluminum, but the density of titanium is 1.7 times higher). The research results were published in the scientific journal Sustainable Materials and Technologies.
Ultra-high purity inorganic materials are widely used in the fields of optics and semiconductors, namely, quantum electronics, energy equipment and manufacturing industries. For inorganic substances, one of the products demanded by the market is ultrahigh-purity alumina (UHPA) powder, which can be used as a precursor for sintering high-quality optical ceramics to produce single crystal aluminum yttrium garnet, synthetic sapphire, and refractory Materials and other high-purity materials, catalysts or adsorbents. The existing method of UHPA production is called the Bayer process. The Bayer process usually allows obtaining chemically pure alumina (99.7%). However, this purity value cannot meet the requirements of the modern optical industry: the total content of impurities in alumina should be less than 103%. Therefore, many researches are devoted to developing new methods to obtain UHPA products.
The main industrial method for obtaining UHPA with a purity of 99.99% is the hydrolysis of aluminum isopropoxide. The alternative method of obtaining UHPA is:
• Thermal decomposition of aluminum nitrate • Electrochemical aluminum dissolution and subsequent heat treatment • Hydrothermal aluminum treatment Metal aluminum with the same ultra-high purity (99.99%) is used as the raw material for all these UHPA production technologies. Although metallic aluminum is an industrial product, the purification of aluminum increases the raw material cost of UHPA production by 5 times. Metal aluminum is more suitable for UHPA production raw materials than alumina, because its purity can be increased from 99.70% to 99.99% through a three-step industrial electrolysis process. The energy consumption of electrolytic refining (Hoopes process) does not exceed the energy consumption of primary aluminum production (Hall-Heroult process). Only by adding 99.99% pure oxygen to metal aluminum, UHPA with a purity of 99.995% can be obtained. In theory, 1 kg of aluminum is converted into 1.89 kg of alumina, so the impurities in the alumina are reduced by about half.
The NUST MISiS team uses aluminum particles with a purity of 99.7%. Through oxidation, alkali and acid treatment, and thermal calcination at 1450°C, the particles are turned into aluminum hydroxide. It should be noted that due to the low cost of raw materials and the cheapest amount of reagents (potassium hydroxide and hydrochloric acid), compared with existing methods, the economic potential of using aluminum pellets as raw materials for UHPA production is undoubtedly high.
At each stage of UHPA powder acquisition, researchers read oxide impurities, especially iron and potassium impurities, which proved to be the most problematic. Based on these data, the team subsequently modified the chemical treatment, washing and calcination to obtain UHPA with a purity of 99.99% and 99.999%.
Double the intensity
Today, there are several technologies for metal printing, mainly selective laser melting (SLM) and selective laser sintering (SLS). Both involve the gradual layering of the metal powder “ink” to build a given volume map. SLS or SLM is an additive manufacturing technology based on layer-by-layer sintering of powdered materials using a powerful laser beam. Although the optimal processing conditions for the powder still need to be determined, the NUST MISiS team has used the material to develop a 3D printed prototype using selective laser melting.
Titanium is the best metal for the manufacture of products in the aerospace industry, but the powder cannot be used for 3D printing because of its fire and explosion hazards. Aluminum is an alternative material because it is light (density 2700 kg/m3) and moldable, with an elastic modulus of approximately 70 MPa. This is one of the main requirements of the industry for metals suitable for 3D printing. However, the strength of aluminum itself is insufficient: even for hard aluminum alloys, the tensile strength is 500 MPa, and the Brinell hardness HB is 20 kgf/mm2.
A research team led by Professor Alexander Gromov of the Non-Ferrous Metals Department of NUST MISIS proposed a solution on how to enhance aluminum 3D printing. Researchers have developed a technology to enhance aluminum-based composite materials obtained by 3D printing, and have obtained innovative precursor modifiers by burning aluminum powder. The combustion products (nitrides and alumina) are nano-layers formed between particles specially prepared for sintering the surface of the branches. The special properties and structure of the surface make the particles firmly adhere to the aluminum matrix, and as a result, the strength of the resulting composite material is doubled.
3D printed parts using ultra-high purity alumina