The kinetics of the FeB/Fe2B layers and diffusion zone at the surface of AISI 316 steels exposed to the powder-pack boriding process were studied in this work. FeB/Fe2B layers and diffusion zone ...measurements were taken at different temperatures and exposure times to validate diffusion-controlled growth during the boriding process. In order to obtain the boron diffusion coefficients at the FeB/Fe2B layers and diffusion zone, a mathematical model based on the mass balance at the growing interfaces was proposed. The activation energy values estimated for the FeB and Fe2B layers were 204 and 198kJmola degree 1 respectively. In addition, the activation energy value obtained for the diffusion zone was 116kJmola degree 1. The diffusion model was extended to estimate the FeB/Fe2B layer thicknesses, and the depth of the diffusion zone at the temperature of 1243K with 3 and 5h of exposure, based on the experimental parameters ascribed to the boriding process. Finally, the effects of the FeB/Fe2B growth and diffusion zone, on the weight gain of borided steels and on the instantaneous velocity of the interfaces were incorporated in the model.
In this study, the fracture toughness of the Fe2B layer was estimated using the Berkovich indentation technique. Boron diffusion at the surface of the AISI 1018 steel was conducted using a ...powder-pack boriding process at a temperature of 1273K with 6h of exposure. The mechanical characterization of the Fe2B layer was performed on three different distances from the surface using a range of indentation loads (10 to 500mN) for each distance. The behavior of the hardness as a function of the indentation load showed the presence of the indentation size effect (ISE) at the different distances from the surface, in which the apparent or real hardness was estimated according to the concept of the Nix and Gao model. Finally, two indentation-cracking models were used to estimate the fracture toughness of the Fe2B layer on the different distances from the surface; the results were ranged from 1.5 to 4.2 MPa m1/2, which denoted the brittleness and the influence of the anisotropic nature of the boride layer.
•The fracture toughness along the depth of the Fe2B layer was evaluated.•The apparent hardness of the boride layer was established by the GND theory.•The fracture resistance of the Fe2B layer is a function of the indentation distance.
New fracture toughness (KC) data for cobalt boride (CoB and Co2B) coatings were obtained using the Vickers depth-sensing microindentation technique. The coatings were developed on the surface of a ...CoCrMo alloy using the powder-pack boriding process at temperatures between 1223 and 1273K using various exposure times for each temperature. The mechanical characterization of the boride coatings was divided into two procedures: first, Vickers indentations were conducted at constant distances from the surface using loads ranging from 15 to 450mN. For the entire set of experimental conditions, the behavior of the indentation load as a function of the diagonal length (dm) was examined on the CoB and Co2B coatings. Second, the crack lengths emanated on the corners of the indentations marks (with applied loads above 250mN) were measured on both coatings using a scanning electron microscope (SEM).
Based on the indentation results, the KC values of the cobalt boride coatings were estimated using the universal crack equation, which is applicable independent of the cracking mode. The results indicated that the CoB and Co2B coatings exhibited two types of cracking modes (intermediate and radial-median, respectively), and that the fracture toughness of the Co2B coating was ten-fold greater than that of the CoB coating.
•New fracture data for cobalt boride coatings were estimated using indentation.•The presence of two cracking modes was observed on the CoB and Co2B coatings.•The fracture values of the coatings were obtained by the universal crack equation.
New results about the evolution of the FeB-Fe2B layers during a diffusion annealing process (DAP) are presented in this work. First, the growth of the boride layers over the surface of an AISI 1045 ...steel was developed by means of the powder-pack boriding process (PPBP) at temperatures of 1173–1273K with different exposure times for each temperature. The boron diffusion coefficients in the FeB and Fe2B were estimated according to the mass balance equations on the growth interphases, and expressed as a function of the boriding temperatures by the Arrhenius equation. Moreover, the DAP was conducted on borided samples obtained at 1273K with 4–8h of exposure using a SiC atmosphere, and considering the theoretical values of annealing times proposed by the extended model. The evolution of the boride layer microstructure was represented by the interphase velocities of the FeB/Fe2B and Fe2B/substrate, and the relationships between the growth of the Fe2B at the expense of the FeB layer for the applied range of annealing times.
•Borided steels were exposed to an annealing process using a SiC atmosphere.•Annealing times were proposed based on the growth kinetics of boride layer.•A complete elimination of the FeB layer was observed after the annealing process.•Kinetic expressions were obtained for the boride layer evolution during annealing.
New results about the tribocorrosion resistance and cytotoxicity of FeB-Fe2B layer developed by the powder-pack boriding process on the surface of AISI 316 L steel are presented in this work. ...Initially, the tribocorrosion tests in the borided AISI 316 L steel and the untreated material (AISI 316 L steel) were performed in Hank's solution, using a ball-on-flat configuration, which was connected with a three electrode-chemical cell. The sliding tests, in the presence or absence of corrosion, were performed under 20N normal force using an alumina ball as a counter body. For the overall experimental conditions, the material loss for each material was estimated according to the ASTM G119 procedure. Further, the in vitro cytocompatibility of FeB-Fe2B layer on AISI 316 L steel and the untreated material was evaluated by the indirect contact method, in which cell lines of immortalized human fibroblast (CHON-002) and normal renal epithelium of Cercopithecus aethiops (Vero) were used.
The results showed that the presence of FeB-Fe2B layer on the AISI 316 L steel improves the tribocorrosion resistance 1.5 times than that of the untreated material, with a presence of a wear-corrosion degradation mechanism in contrast with a wear-dominated regime for the untreated material. Finally, the cytotoxicity tests revealed satisfactory properties in terms of effects on survival and proliferative activity of human fibroblasts and Vero cells on the surface of the borided AISI 316 L steel.
•New results about the tribocorrosion resistance of FeB-Fe2B layer were obtained.•A wear corrosion dominated-regime was estimated for the borided AISI 316 L steel.•Contribution of synergy to the total material loss was reduced by the boride layer.•The FeB-Fe2B layer revealed good cytocompatibility with Vero and CHON-002 cells.
High-temperature coatings are commonly used in components working at high temperatures, such as turbine blades and combustion chambers to increase their efficiency. The durability of the ...high-temperature coatings is governed mainly by the growth of the thermally grown oxide (TGO) layer. In the present study, the effect of the addition of SiC microfibers on microstructural stability, adhesion and oxidation resistance of thermal barrier coatings (TBC) subjected to thermal cycles at high temperature was investigated. High-velocity oxy-fuel (HVOF) and air plasma spraying (APS) thermal spraying processes were used to produce bond coat (BC-NiCoCrAlY) and ceramic (yttria-stabilized zirconia-8YSZ) respectively. The adhesion test was determined accordingly to ASTM-C-633 Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were employed to characterize the morphology, microstructure, and phases of the coatings. After 10 cycles at 25 h at 1100 °C, reinforced samples with 3 wt% SiC microfibers showed better oxidation resistance compared to those without the addition of SiC microfibers. Also, was noted that Si compounds were distributed along some cracks at the interface of the TGO-TBC, enhancing its adherence.
•Better thermal oxidation resistance of SiC-reinforced samples•Interfacial TGO/TC adherence improved by auto-healing process•Formation of stable silicon oxides additional to TGO oxygen barrier•Auto-healing products delaying or blocking crack propagation•SiC-reinforced samples a lower growth of TGO layer
In this study, new data about the growth kinetics and indentation properties of cobalt boride layers formed on the surface of the ASTM F-75 biomedical alloy were estimated. The boron diffusion at the ...surface of the biomedical alloy was conducted using a powder-pack boriding process at temperatures of 1223–1273K with different exposure times for each temperature. Two mathematical approaches were proposed to determine the boron diffusion coefficients of the CoB and Co2B layers in the range of boriding temperatures, in which the experimental results of the kinetics of the cobalt boride layers were compared with those estimated using diffusion models.
Finally, the mechanical characterization of the cobalt boride layers was evaluated by indentation techniques with applied loads of 0.98N and 50mN, respectively. According to the nanoindentation tests, a maximum hardness value (30GPa) and a maximum Young's modulus (380GPa) were obtained near the surface region (5μm) of the borided cobalt alloy.
•New data about the growth kinetics of cobalt boride layers were estimated.•The diffusion models can be adopted to determine the thickness of the boride layer.•Indentation properties were evaluated along the depth of the CoB and Co2B layers.•Vacuum aging should be the preferred aging method for most of the beef industry.•Vacuum aging should be the preferred aging method for most of the beef industry.
In this work, the tribological performance of borided and untreated AISI H13 steels under dry and lubricated conditions was studied. The formation of the boride layer on the AISI H13 steel was ...conducted using the powder-pack boriding process at 950 °C for 6 h of exposure. The tribological performance was studied by reciprocating sliding wear tests, conducted with an alumina ball establishing a sliding distance of 100 m and a speed of 30 mm s
−1
. The normal loads in dry tests varied from 10 to 25 N, compared with the loads ranged from 75 to 150 N under lubricated conditions (SAE 10W-40). The results showed that under dry conditions, the coefficient of friction (COF) ranged between 0.59 and 0.68 for the borided AISI H13 steel, and from 0.64 to 0.71 for the untreated H13 steel; the wear rates, at 25 N, were estimated around of
0.8
×
10
-
5
and ~
6
×
10
-
5
mm
3
N
−1
m
−1
, respectively. In contrast, using lubricant, the COF decreased to values from 0.10 to 0.11, for both materials, in which the wear rates decreased one order of magnitude. Finally, for the overall set of experimental conditions, failure mechanisms such as smearing, cracking, pitting and plastic deformation were identified.
New results about the wear resistance of CoB-Co
2
B coatings under dry sliding conditions were estimated in this work. The cobalt boride coatings were developed at the surface of the ASTM F1537 alloy ...by means of the powder-pack boriding process using two experimental conditions: 1223 K with 6 h of exposure and 1273 K with 10 h of exposure. Before the sliding wear tests, Vickers depth-sensing microindentation tests were conducted on the cross section of the cobalt boride coatings to estimate the distribution of hardness, Young’s modulus, and residual stresses. Otherwise, the sliding wear tests were performed on both boriding conditions and on the untreated material, using a ball-on-flat configuration comprised of an alumina ball as a counterpart with applied loads between 5 and 20 N. The wear rates of the borided ASTM F1537 alloy were ranged between 4.02 and 8.91 × 10
−6
mm
3
N
−1
m
−1
compared with the values of the untreated material (13.90 and 15.78 × 10
−6
mm
3
N
−1
m
−1
) for the overall set of experimental conditions; nevertheless, the influence of boriding conditions (1273 K with 10 h of exposure) tended to increase the CoB coating thickness, developing a more brittle layer that decreased the sliding wear resistance at the surface of the borided ASTM F1537 alloy. Finally, the presence of failure mechanisms on the surface of the wear tracks was analyzed for both borided ASTM F1537 alloy and untreated material.
In this study, new results about the practical adhesion resistance of boride coating/substrate system formed at the surface of AISI 316 L steel and improved by means of a diffusion annealing process ...are presented. First, the boriding of AISI 316 L steel was performed by the powder-pack method at 1173 K with different exposure times (4-8 h). The diffusion annealing process was conducted on the borided steels at 1273 K with 2 h of exposure using a diluent atmosphere of boron powder mixture. The mechanical behavior of the boride coating/substrate system developed by both treatments was established using Vickers and Berkovich tests along the depth of the boride coatings, respectively. Finally, for the entire set of experimental conditions, the scratch tests were performed with a continuously increasing normal force, in which the practical adhesion resistance of the boride coating/substrate system was represented by the critical load. The failure mechanisms developed over the surface of the scratch tracks were analyzed; the FeB-Fe
2
B/substrate system exhibited an adhesive mode, while the Fe
2
B/substrate system obtained by the diffusion annealing process showed predominantly a cohesive failure mode.