•Borided AISI 316L steels were evaluated numerically by the pin-on-disc test.•Adaptive non-linear re-meshing was used during the wear test.•Compressive and tensile stresses were located within the ...contact area after wear.
In this study a numerical-experimental evaluation of the sliding wear resistance of iron boride layers formed on the surface of an AISI 316L steel was developed. The boriding process was carried out at a temperature of 900 °C for 2 h and 6 h of exposure. Pin-on-disc tests were realized on non-borided and borided AISI 316L steels. The experimental results showed that the boriding contributed significantly to the wear resistance of the AISI 316L steel compared to the non-borided material. In addition, the thinner boride layer thickness developed more severe wear mechanisms. Finally, principal stresses and maximum shear stress generated in the layer/substrate systems were evaluated during the wear test using the finite element method (FEM).
New results about the scratch adhesion resistance of nickel boride layer on Inconel 718 superalloy were estimated in the present study. The nickel boride layer was developed on the surface of Inconel ...718 superalloy by means of the powder-pack boriding process conducted at 1173K with 2, 4, and 6h of exposure. The microstructure of the nickel boride layer was analyzed from optical microscopy, X-ray diffraction and energy dispersive spectroscopy (EDS). Furthermore, and before the scratch tests, indentation properties of the nickel boride layers such as hardness, Young's modulus, and the distribution of residual stresses were evaluated using Berkovich nanoidentation tests applying a constant load (50mN) across the diffusion layers. The scratch tests were performed over the surface of the nickel boride layer-substrate systems using a Rockwell-C diamond indenter with a continuously increasing normal force from 1 to 80N, whereas the behavior of the coefficient of friction and the residual depth as a function of the scratch length were monitored during the tests. For the determination of the critical loads, the combination of acoustic emission signal with microscopic observations of the worn tracks were used; the critical loads were estimated at which the layer cracks (cohesive failure) or is detached (adhesive failure) and they explained according to the mechanical properties of the nickel boride layer-substrate system. For all the set of experimental conditions, the presence of three types of failure mechanisms over the worn tracks were detected, while the results showed that the critical loads increase with enhancing nickel boride layer thickness.
•New results about the adhesion resistance of nickel boride layer were obtained.•From scratch test, the critical loads of the layer-substrate system were estimated.•Tensile residual stresses decrease the practical adhesion resistance of the layer.•The adhesion resistance increases as a function of the boride layer thickness.•Hertzian cracking, chipping and spalling were observed over the scratch tracks.
An experimental-numerical study of the contact fatigue resistance of AlCrN coatings formed on an AISI 4140 steel was performed. Three different coatings were formed: a coating of aluminum chrome ...nitrides (AlCrN) by a physical vapor deposition process (PVD) with a thickness of 2.2 ± 0.3 μm, a layer of iron nitrides (FexN) by a gas nitriding process with a compound layer of 10 ± 1 and an underlying diffusion zone of 65 ± 4 μm and finally a duplex system of AlCrN/FexN with a thickness of 3.0 ± 0.2 μm of AlCrN, a compound layer with a thickness of 2.5 ± 0.3 μm and 16 ± 3 μm of the diffusion zone. Contact fatigue tests were performed on a MTS Acumen electrodynamic test system, by applying cyclic loading to each of the coatings using a sphere to generate Hertzian contact stresses. The contact fatigue test methodology consisted of two main stages. First, the critical load of each formed system was obtained by means of the application of monotonic loads, where the monotonic load value in which the first circular cracks on the coating surface were observed was set as the critical load. The critical loads of the three coatings were: FexN: 800 N, AlCrN: 1000 N and AlCrN/ FexN: 1100 N. Second, fatigue conditions were performed up to 100,000 cycles using subcritical loads with a frequency of 5 Hz. Cohesive damage was observed in the samples containing iron nitrides, whilst delamination was caused on the AlCrN single layer coating. A numerical model based on the finite element method was developed to evaluate the stress field generated in the systems by cyclic contact loading. The thinner thickness and the abrupt transition of mechanical properties from the coating to substrate caused the maximum principal stress to be located within the contact zone in the AlCrN single layer coating. Results showed better resistance to contact fatigue in the AlCrN/FexN duplex system because of the presence of the intermediate layer of iron nitrides.
•AlCrN/FexN coatings were evaluated by standing contact fatigue.•Influence of nitride layer in the duplex system under contact fatigue was analyzed.•Failure mechanism was less severe in the duplex system under contact loading.•Contact stresses were related with failure mechanisms observed in the coatings.•Nitride layer in the duplex system avoid the adhesive failure of coating.
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.
•Borided AISI H13 steels were evaluated by the scratch test.•Influence of indenter tip radius on failure mechanisms was studied.•The smaller indenter tip radius generated more severe damage.
In this ...work, the influence of indenter tip radius (ITR) on scratch tests in boride layers was studied. The thermochemical treatment of boriding was performed on an AISI H13 steel at 1000 °C for 1 h. Depth sensing indentation test was developed to estimate both, hardness, and elastic modulus of the boride-layer/substrate system. Indenter radius of 200, 100, 50 and 20 μm were used for the scratch tests on borided steel. Failure mechanisms were analyzed by scanning electron microscopy (SEM). Predominant failure mechanisms were lateral cracking, chipping, and gross chipping. ITR of 20 μm developed more severe damage on the borided AISI H13 surface and the more severe substrate plastic deformation was obtained by ITR of 200 μm.
In this work, an experimental-numerical evaluation of the standing contact fatigue testing of a nitrided AISI 316L steel was developed. The nitride layers were formed at the surface of an AISI 316L ...steel by a salt bath nitriding process at a temperature of 580 °C for 1, 3 and 5 h of exposure time, obtaining three different layer thicknesses. In order to know the mechanical response and the different mechanisms of damage associated with the standing contact fatigue test, Hertzian tests were performed on a MTS machine by cyclic loading of a sphere on a flat surface formed by the layer/substrate system. The standing contact fatigue test was developed through two main stages. First, the critical loads for each treatment condition were determined by monotonic tests, where the appearance of circular cracks was considered as the failure criterion. Subsequently, cyclic subcritical loads were applied at a frequency of 5 Hz. A numerical model based on the finite element method was developed to evaluate the stress field generated in the system by cyclic contact loads. The results indicate that the thinnest thickness of nitride layer exhibits better resistance to standing contact fatigue.
•Nitride layers were evaluated through standing contact fatigue.•The stress field associated with contact damage modes in the nitride layers was obtained by the finite element method.•Cohesive damage was a function of both the range of the maximum principal stress and the amplitude of the radial distance.
Characterization of AISI 4140 borided steels Campos-Silva, I.; Ortiz-Domínguez, M.; López-Perrusquia, N. ...
Applied surface science,
02/2010, Letnik:
256, Številka:
8
Journal Article
Recenzirano
Odprti dostop
The present study characterizes the surface of AISI 4140 steels exposed to the paste-boriding process. The formation of Fe
2B hard coatings was obtained in the temperature range 1123–1273
K with ...different exposure times, using a 4
mm thick layer of boron carbide paste over the material surface. First, the growth kinetics of boride layers at the surface of AISI 4140 steels was evaluated. Second, the presence and distribution of alloying elements on the Fe
2B phase was measured using the Glow Discharge Optical Emission Spectrometry (GDOES) technique. Further, thermal residual stresses produced on the borided phase were evaluated by X-ray diffraction (XRD) analysis. The fracture toughness of the iron boride layer of the AISI 4140 borided steels was estimated using a Vickers microindentation induced-fracture testing at a constant distance of 25
μm from the surface. The force criterion of fracture toughness was determined from the extent of brittle cracks, both parallel and perpendicular to the surface, originating at the tips of an indenter impression. The fracture toughness values obtained by the Palmqvist crack model are expressed in the form
K
C
(
π/2)
>
K
C
>
K
C
(0) for the different applied loads and experimental parameters of the boriding process.
AISI 316L borided steels under cyclic contact loading were evaluated. Boriding was carried out by two powder-pack processes: the continuous and interrupted processes. Boriding processes were ...developed at 900 °C for 1 h (continuous process) and 4 h (interrupted process). A monolayer mainly formed by Fe2B was obtained by the interrupted boriding with a thickness of 6.09 ± 0.31 μm and a surface hardness of 22.3 ± 1.4 GPa. In contrast, a FeB-Fe2B bilayer was formed by the continuous boriding with a total thickness of 13.08 ± 0.39 μm and a surface hardness of 26.3 ± 2.1 GPa. Adhesion tests were developed, in which the monolayer showed better adhesion than that the bilayer. Cyclic contact tests were carried out by loading a ball on the borided steel surface. Circular cracks because of the applied critical load (monotonic load) were observed on the borided steel surface. Subcritical loads were applied to the borided steels, where cohesive damage was caused in the bilayer, whereas no damage was observed in the monolayer at low subcritical loads. In contrast, circular cracks were observed in both treatment conditions at high subcritical loads. In addition, the high percentage of the FeB phase caused a more severe damage upon the bilayer system. Additionally, the thinner thickness of the boride layer, as well as the presence of compressive residual stresses (−0.75 GPa) in the monolayer system, caused a decrease on the maximum principal stress (2.4 GPa at the highest applied load) caused by contact loading compared to bilayer system (5.2 GPa at the highest applied load). Therefore, the interrupted boriding (monolayer system) showed a better mechanical resistance under cyclic contact loads than the continuous boriding (bilayer system).
•FeB-Fe2B and Fe2B layers were obtained by continuous and interrupted boriding.•The bilayer system showed more severe damage under cyclic contact loads.•The plastic deformation of the substrate decreased the damage in the monolayer system.
•Strain hardening exponents n of borided and nitrided layers were calculated.•Boriding time had a negligible effect on strain hardening exponent.•A longer boriding time decreased the plastic work of ...indentation.•A short boriding time presented better standing contact fatigue performance.•The nitride layer withstands mechanical loading without spallations.
In this study, boride and nitride layers formed on H13 steel were assessed by cyclic spherical contacts. Boriding was conducted at 800 °C for 1 and 5 h, and nitriding at 580 °C for 1 h. The hardness and strain hardening exponents n of the layers were estimated by spherical indentations (5 µm radius). The standing contact fatigue (SCF) performance was investigated by cyclic spherical contacts (Al2O3, 3 mm diameter), first applying monotonic load tests from 300 to 1000 N to establish the critical loads considering the onset of certain cracks for each layer; later, between 102 and 105 cycles applying different subcritical loads. The results revealed strain hardening exponents of nB1h = 0.226, nB5h = 0.230 and nN1h = 0.241. In SCF, a critical load of 600 N in both layers was found. In cyclic tests, the thicker boride layer presented larger cracking and moderate spallations, attributed to its mechanical properties; the thinner layer exhibited a better SCF resistance. Regarding nitriding, well-defined circumferential cracks without spallations were observed.
New data for micro-abrasion wear resistance of CoB/Co2B coating was obtained through a ball cratering test. The coating was formed on the surface of a CoCrMo alloy using the powder-pack boriding ...method. The boriding process was carried out at 1223K over 5h of treatment resulting in the formation of CoB/Co2B coating with a total thickness of 28μm approximately. Both hardness and Young's modulus profile through the cobalt borides were evaluated by Berkovich depth-sensing indentation using a load of 25mN. The wear coefficients of CoB and Co2B formed on CoCrMo alloy were evaluated by a Plint TE-66 micro-abrasion tester using SiC particles dissolved in deionized water as abrasive slurry. The results demonstrated that the cobalt borides have wear coefficients higher than CoCrMo and improve their micro-abrasion wear resistance. Furthermore, a wear-mode map was developed to identify the two and three body abrasion mechanisms and the transition between them modifying the concentration of SiC in the slurry and the magnitude of applied load.
•New wear resistance data for cobalt borides were estimated by micro-abrasion tests.•The wear coefficients were determined for CoB and Co2B phases.•The wear-mode map was obtained for CoB phase.•The two-body, three-body, and mix mode wear mechanism were identified in CoB phase.
