Sukru Taktak

Identification of delamination failure of boride layer on common Cr-based steels

Adhesion is an important aspect in the reliability of coated components. With low-adhesion of interfaces, different crack paths may develop depending on the local stress field at the interface and the fracture toughness of the coating, substrate, and interface. In the current study, an attempt has been made to identify the delamination failure of coated Cr-based steels by boronizing. For this reason, two commonly used steels (AISI H13, AISI 304) are considered. The steels contain 5.3 and 18.3 wt.% Cr, respectively. Boriding treatment is carried out in a slurry salt bath consisting of borax, boric acid, and ferrosilicon at a temperature range of 800–950 °C for 3, 5, and 7 h. The general properties of the boron coating are obtained by mechanical and metallographic characterization tests. For identification of coating layer failure, some fracture toughness tests and the Daimler-Benz Rockwell-C adhesion test are used.

A diffusion model for the titanium borides on pure titanium

In the present study, commercial pure titanium was successfully plasma paste borided using borax paste at a temperature of 700, 750 and 800°C for 3, 5 and 7 h. The X-ray diffraction and scanning electron microscopy techniques revealed the presence of both TiB2 top-layer and TiB whiskers sub-layer. The formation rates of the TiB2 layer and TiB whiskers were found to have a parabolic character at all applied process temperatures. Based on the present Ti borides growth data, correspondent diffusion temperature and time, an analytical diffusion model was used to estimate boron diffusion coefficients and activation energies of the boride phases in a binary multiphase Ti–B system. Depending on the temperature and layer thickness, the activation energies of boron in TiB2 and TiB phases were determined to be 137.55 ± 0.5 and 55.21 ± 0.5 kJ mol−1, respectively. These values of boron activation energies for pure titanium were compared to the literature data.

Characterization and Rockwell-C adhesion properties of chromium-based borided steels

In this study, adhesion properties of boride layers formed on the surface of AISI 52100, AISI 5140, AISI 440C, AISI 420 and AISI 304 steels were investigated. Boronizing treatment was carried out in Ekabor-II powders at the temperatures of 850 and 950 °C for 4 h. The properties of boride layers were evaluated by optical microscopy, SEM, X-ray diffraction and micro-Vickers hardness tester. The Daimler-Benz Rockwell-C adhesion test was used to assess the adhesion of boride layers. Test result showed that adhesion of boride layers depended on the dual-phase structure. The stresses at the FeB/Fe2B interphase caused delamination failure and poor interphase adhesion with increase in the depth of hard and brittle FeB-based layer.

Effect of pulse plasma nitriding on tribological properties of AISI 52100 and 440C steels

AISI 52100 and 440C bearing steels were nitrided in conventional plasma (CPN) and pulsed plasma (PPN) consisting of 0.33 and 1 N2/H2 gas ratios at temperature of 500°C for 4 h under a constant pressure of 5 mbar. The surface of nitrided steels was investigated using optical microscopy, X-ray diffraction (XRD) and microhardness. The tribological behaviour of plasma nitrided steels was studied by means of unlubricated ball-on-disc method under constant loads of 5 and 20 N, sliding speed of 0.3 m/s at room temperature. The SEM and EDS techniques were used to analyse the worn surfaces of the steels. The results showed that γ′-Fe4N and α-Fe(N) were dominant phases for pulsed plasma nitrided 52100 and 440C steels, respectively and pulsed plasma nitriding slightly improved the wear behaviour of both steels.

Synthesis of Ag-doped hydrogenated carbon thin films by a hybrid PVD–PECVD deposition process

Silver-doped hydrogenated amorphous carbon (Ag-DLC) films were deposited on Si substrates using a hybrid plasma vapour deposition–plasma enhanced chemical vapour deposition (PVD–PECVD) process combining Ag target magnetron sputtering and PECVD in an Ar–CH4 plasma. Processing parameters (working pressure, CH4/Ar ratio and magnetron current) were varied to obtain good deposition rate and a wide variety of Ag films. Structure and bonding environment of the films were obtained from transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy studies. Variation of processing parameters was found to produce Ag-doped amorphous carbon or diamond-like carbon (DLC) films with a range of characteristics with CH4/Ar ratio exercising a dominant effect. It was pointed out that Ag concentration and deposition rate of the film increased with the increase in d.c. magnetron current. At higher Ar concentration in plasma, Ag content increased whereas deposition rate of the film decreased. FTIR study showed that the films contained a significant amount of hydrogen and, as a result of an increase in the Ag content in the hydrogenated DLC film, sp2 bond content also increased. The TEM cross sectional studies revealed that crystalline Ag particles were formed with a size in the range of 2–4 nm throughout an amorphous DLC matrix.

Wear behaviour of TRD carbide coatings at elevated temperatures

Purpose – The purpose of this paper is to characterize carbide coatings obtained by thermo reactive diffusion (TRD) method on AISI 52100 and 440C bearing steels, which are extensively used in industry, and to study wear behaviour of coated steels at elevated temperatures.Design/methodology/approach – For coatings of vanadium and titanium carbides, TRD treatment is performed on AISI 52100 and 440C steels using pack method at 950°C for 3 h. Carbide coatings are characterized using X‐ray diffraction (XRD). The Daimler‐Benz Rockwell‐C adhesion test and micro‐Knoop indenter is used to assess the adhesion and hardness of the carbide layers, respectively. Ball‐on‐disc arrangement is used for determination of tribological properties of carbide‐coated steels. Friction and wear tests are carried out against Si3N4 ball at elevated temperatures up to 600°C under 5 N load, for sliding speed of 0.3 m/s.Findings – The presence of carbides formed on AISI 52100 (Ti6C3.75 and VC0.88 phases) and on AISI 440C (Ti6C3.75, VC0....

Characterization of nanocomposite a-C:H/Ag thin films synthesized by a hybrid deposition process

Silver containing amorphous carbon films were deposited on Si wafer using a hybrid deposition process combining d.c. magnetron sputtering and PECVD. The concentration of Ag in the films was varied from 1.3 to 8.3 at % by changing d.c. magnetron current of Ag target. The influence of incorporated Ag in the a-C:H on the atomic bond structure of the films were investigated by XPS, FTIR, Raman, and HRTEM methods of analysis. The XPS, FTIR, and Raman studies demonstrated that as the silver concentration increased in the a-C:H, sp2 bonding content increased and a-C:H films changed to more graphitic structure. The high resolution TEM cross sectional studies revealed that crystalline Ag particles formed with a size in the range of 2–4 nm throughout an amorphous a-C:H matrix.

Fracture Toughness of Plasma Paste-Borided Layers Produced on Nickel-Based Alloys

The boriding treatment is the suitable process which caused an increase in surface hardness and wear resistance of nickel and its alloys. However, the phase composition of boride layers strongly influences on layer properties—especially hardness and brittleness. The method of plasma paste boriding was used in this study to produce the hard boride layers on nickel-based alloys: Ni201, Inconel 600, and Nimonic 80A. This process was carried out at 800 °C (1073 K) for 3 h. The chemical composition of substrate material was the reason for producing of layers which were characterized by different thickness: 55 μm for Ni201, 42 μm for Inconel 600, 35 μm for Nimonic 80A. The lowest hardness (1000–1400 HV) and the highest fracture toughness (up to 2.6915 MPa m1/2) were measured for layer produced on Ni201. In this specimen, only nickel borides were detected. However, due to high content of chromium, in case of Inconel 600-alloy and Nimonic 80A-alloy, the higher hardness (in the range of 1000–2450 HV) and higher brittleness (average value of K c = 0.77 MPa m1/2 for Inconel 600-alloy and K c = 0.67 MPa m1/2 for Nimonic 80A-alloy) were calculated. This situation was caused by the appearance of hard ceramic phases (chromium borides CrB and Cr2B) in borided layer. Simultaneously, at the cross section of each sample, the strong fluctuation of hardness occurred, due to the variable participation of chromium and nickel borides.