International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This part is a continuation of Part-1, which was studying the effect of anti-corrosion nano-materials coating using zinc (Zn) and cobalt (Co) on corrosion resistance and its relationship with mechanical properties. While, part 2 was on studying the linear stresses resistance after coating by using the same nanomaterials of paret-1 of carbon steel pipe and their relationship with chemical corrosion resistance using finite element analysis (FEA). The coating was tested with different thicknesses of nano-layers (300 μm, 600 μm, 900 μm, 10 μm) on a thick-walled cylindrical pipe subjected to a uniformly distributed internal pressure of 4 bars. The results showed that the value of linear normal stresses did not change when coating with 300 μm for both nano-coating materials. However, it was started to decrease slightly when covered with 600 μm of cobalt and continues to decrease with increasing the coating thickness. In addition, the results have shown that the overall improvement in linearized normal stresses and corrosion resistance due to cobalt coating can be about (66 %) higher in comparison with Zinc at 10 μm thickness of coating.

The work is devoted to the study of evolution of flaws in aluminium alloys of Al-Zn-Mg-Cu, Al-Cu-Mg-Мn alloying systems and to the determination of their connection with structural factors of the material such as the size and composition of intermetallic phases conditioned by heat treatment tempers, and also to the study of the effect of big number of physical factors on the long-term behaviour of structural elements of aluminium alloys, and to the determination of the rate of formation of corrosion damages in structural elements of the aircraft wing

ECAP was conducted using route Bc with an angle of 120° between the die channels and a stepwise decrease of temperature from the initial 425 °C to 300 °C at the final, 12th pass. The cumulative equivalent strain the ECAP billets underwent was about 7.8. The structure examination showed that ultrafine-grained structure with the grain size of 0.69 – 1 μm was formed during ECAP process. In addition, particles of the phase Mg12Nd with an average size of 0.45 μm were formed. The refinement of the microstructure resulted in an improvement of the mechanical properties of the alloy. After ECAP, the strength characteristics of the alloy increased to the levels of ultimate tensile strength of 300 and yield strength of 260 MPa to be compared to those for the initial state (220 MPa and150 MPa, respectively). At the same time, the ductility increased to 13.2 %, which compares favourably with the initial value of 10.5 %. The ECAP process does not affect the resistance to electrochemical corrosion. The rate of chemical corrosion was found to be reduced owing to the ECAP processing.

The report provides examples of two innovative solutions using nitrogen-containing steels. The use of nitrogen-containing steels allows to increase the durability and reliability of products; to reduce the thickness of work sections; to reduce the cost of maintenance and repair downtime. The proposed solutions: 1. Austenitic corrosion resistant cast steel with 0,5%N. After homogenizing heat treatment the steel surpasses traditional cast austenitic steels at yield strength at ~1.5-2 times, impact toughness ~ 4.5 times, hardness – by about 25%. It is recommended for the manufacture of cast valves. 2. The martensitic steel grade with 0,11-0,17% N. This steel is well proved as a material for the manufacture by cold heading of very high strength corrosion resistant fasteners.

Researched were the physico-chemical properties, hardening and corrosion resistance of Cr₁₈Ni₁₀N type austenitic chromium- nickel stainless steels of different purity by the impurities and with different nitrogen content: from impurity level to 0.220%. It is demonstrated that nitrogen alloying is beneficial both for hardening and improvement of corrosion resistance of steel under conditions when nitrogen has the form of solid solution. Addition of 0.186-0.220% of nitrogen doesn’t reduce intercrystalline corrosion in standard environment of 0.5M H₂SO₄ + 0.01M KSCN and improves resistance to general and pitting corrosion in chloride-containing environments.

Pure nitric steel shows higher resistance to intercrystalline, general and pitting corrosion in chloride solutions than normal purity steel.

The hardening and austenite stability as a result of nitrogen alloying steel type of Cr₁₈Ni₁₀ in the temperature range, which is usual for the application of such steels as corrosion-resistant structural heat-resistant and/or cryogenic ones was studied. It is shown that the nitrogen alloying is perspective for strengthening and increasing of stability of austenitic stainless steels. Additional strengthening due to the preliminary cold or warm deformation hardening increases a tendency to the martensite formation under load, which limits the operating temperature of these steels. High-strength non-magnetic nitrogen-alloyed steels on the base of Cr₁₈Ni₁₀ steels containing up to 0.22 % of nitrogen are suitable for cryogenic application of non-deformed articles only. Otherwise, a strain-induced martensite will always form in them at temperatures below -70 °С. High strength, ductility and toughness of these steels can be achieved simultaneously only as a result of the TRIP-effect or fine-grained structure formation.

Technique and equipment for plasma spraying of wear-resistant and corrosion-resistant coatings with enhanced adhesive strength was developed. Ceramic powders coated metal thin films were used for plasma spraying. Optimal conditions for deposition of the metal films on the particles of alumina powder (40…63µm fraction) by PVD process were obtained. Deposition of two- layer films on the powder particles was carried out. The first layer was titanium and the second layer was aluminum or copper. The titanium as adhesively-active element capable of wet alumina is necessary for increase the adhesion strength vacuum films as well as plasma sprayed coatings.

A special plasma-spray gun with external arc working in a mode of laminar plasma argon jet generation was designed. Such regime provides melting of the refractory ceramic core, saving metal films as well as localization of thermal effects during spraying process.
The results of testing coated specimens confirmed that the developed technique improves the physical and mechanical properties of the plasma sprayed composite coatings. The sprayed composite coatings were compared with coatings sprayed using pure alumina powders in terms of adhesion, wear and corrosion properties. The shear adhesion strength increases up to about 1.9 times, the wear resistance increases about 5 to 7 times, the corrosion resistance increases about 2.5 to 5 times.

The shear adhesion strength was measured at tension of coated specimen at room temperature by developed adhesion testing technique. The substrate was flat and dog-bone-shaped. The substrate with rectangular cross-section was partially coated with plasma- sprayed coating. The specimens were tested in uniaxial tension under displacement control. The tensile specimens were loaded to adhesion delamination of the coating. Sprayed coating was detached as a result of shear interface stresses.

ECAP was conducted using route Bc with an angle of 120° between the die channels and a stepwise decrease of temperature from the initial 425 °C to 300 °C at the final, 12th pass. The cumulative equivalent strain the ECAP billets underwent was about 7.8. The structure examination showed that ultrafine-grained structure with the grain size of 0.69 – 1 μm was formed during ECAP process. In addition, particles of the phase Mg12Nd with an average size of 0.45 μm were formed. The refinement of the microstructure resulted in an improvement of the mechanical properties of the alloy. After ECAP, the strength characteristics of the alloy increased to the levels of ultimate tensile strength of 300 and yield strength of 260 MPa to be compared to those for the initial state (220 MPa and150 MPa, respectively). At the same time, the ductility increased to 13.2 %, which compares favourably with the initial value of 10.5 %. The ECAP process does not affect the resistance to electrochemical corrosion. The rate of chemical corrosion was found to be reduced owing to the ECAP processing.