Indentation Fracture Toughness Tests Research Articles

Investigation of the failure behaviour of equiatomic AlCrCuNiFe based high entropy alloy TIG weld cladding

The present research focuses on the development of an equiatomic AlCrCuNiFe high entropy alloy (HEA) cladding using the TIG welding process. The influence and contribution of TIG cladding process parameters (welding current, welding speed, and SOD) on the microhardness and flexural stress have been investigated using the response surface methodology (RSM) and analysis of variance (ANOVA), respectively. The indentation fracture toughness test has been conducted over the claddings exhibiting minimum, maximum, and optimum microhardness values. The result revealed that welding current has the highest effect on the mechanical performance of the HEA cladding. The FE-SEM, optical microscopy, XRD and EDS analysis were performed to characterize the claddings. The cladding deposited at the S12 test run offered the least flexural resistance, microhardness, and indentation fracture toughness which was about 812 MPa, 494.97 HV0.3, and 1.29 ± 0.04 MPa.m1/2, respectively. In contrast, the optimized S5 cladding specimen exhibited good flexural resistance, appreciable microhardness and indentation fracture toughness of about 1543.92 MPa, 712 HV0.3, and 1.63 ± 0.03 MPa.m1/2 respectively. The optimum cladding exhibited flexural stress, microhardness, and fracture toughness enhancement of 46.77 %, 30 %, and 26.35 % compared to the least resistance cladding (S12) due to the high-retained alloying elements leading to enhanced solid solution strengthening. The three-point bend-tested cladding specimens’ optical microscopy images revealed that the cladding failure was primarily due to cohesive failure, crack progression, and delamination.

Investigation on structural, mechanical and tribological properties of plasma sprayed Al2O3-40% TiO2 coating

The present work deals with tribological investigation of Al2O3-40% TiO2 coating deposited using plasma spraying. The structural characterization of coating was done using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). The micro hardness was measured by vickers micro hardness tester whereas fracture toughness was determined by Indentation Fracture Toughness Test (IFT) method. The sliding wear tests were carried out at different test conditions involving simultaneous variation of load (P) ranging from 5 to 30 N and sliding velocity (V) ranging from 0.1 m/sec to 0.6 m/sec. The sliding wear rate increased with increasing parameter P × V and friction coefficient displayed minima at a load of 20 N and sliding velocity of 0.4 m/sec. The flash temperature showed the increasing trend with P × V parameter. The variation in coefficient of friction and wear rate with varying test conditions was associated with change in wear mechanism from plastic grooving to delamination of splats & splat fracture and formation & removal of tribo layer of Ti2O3 and Ti3O5 on worn surface.

Effect of A Rapid-Cooling Protocol on the Optical and Mechanical Properties of Dental Monolithic Zirconia Containing 3-5 mol% Y2O3.

Many attempts have been made to improve the translucency of zirconia in dentistry. The purpose of this study was to evaluate the effect of a rapid-cooling heat treatment on the optical and mechanical properties of dental monolithic zirconia. Zirconia containing 3, 4, and 5 mol% Y2O3 were sintered, sectioned, and polished. The specimens were rapidly cooled from high temperature inducing a diffusionless cubic-to-metastable tetragonal (t’) phase transformation. The changes in L*a*b* color coordinates, translucency parameter (TP), and total transmittance (T%) were measured. Three-point bending strength, Vickers hardness, and indentation fracture toughness tests were performed. Quantitative phase analyses were carried out by X-ray diffraction with Rietveld refinement. Scanning electron microscopy (SEM) images were obtained. With increasing Y2O3 contents, TP and T% values increased while strength and toughness decreased. The Rietveld analysis showed that the amount of t’-phase increased after rapid-cooling and annealed 5Y-partially stabilized zirconia (PSZ) contained the highest amount of t’-phase (64.4 wt%). Rapid-cooling improved translucency but the translucency of annealed 5Y-PSZ did not approach that of lithium disilicate glass-ceramic. Rapid-cooling decreased flexural strength significantly, being 306.1 ± 61.8 MPa for annealed 5Y-PSZ. SEM revealed that grains tended to get larger after rapid-cooling. A rapid-cooling treatment can produce t’-phase which can contribute to an increase in translucency but has a negative effect on the mechanical properties of zirconia.

Determination of Vickers indentation fracture toughness of boronised alloyed ductile iron

ABSTRACTIn the present study, copper (Cu), nickel (Ni), and molybdenum (Mo)-alloyed ductile iron was pack boronised at 800–850°C for 3–6 h and subsequently the microhardness and the microstructures of boride layers under different process parameters were investigated in detail. Further, Vickers indentation fracture toughness tests were executed on borided surfaces under 200 g load. The fracture toughness of borided layers was estimated separately by a series of equations and the half-length of corner cracks and the half diagonals of Vickers indents were used as variables. Generally, the values of the obtained fracture toughness were found to be higher than those of previous studies. It was found that thinner boride layers were formed at lower boronising temperatures. The highest toughness value and the thickest boride layer were obtained in the sample boronised at 850°C for 6 h.

Effect of the diffusion annealing process in the indentation properties of cobalt boride layer

New results about the indentation properties of cobalt boride layer exposed to a diffusion annealing process (DAP) are presented in this study. Initially, the cobalt boride layer (CoB-Co2B) was developed at the surface of the ASTM F1537 alloy using the powder-pack boriding process (PPBP) at 1273 K with 6 h of exposure. The DAP was conducted on the borided ASTM F1537 alloy considering the theoretical values (temperature and exposure time) estimated by a diffusion model to dissolve entirely the CoB layer. After that, the distribution of hardness, Young's modulus, and residual stresses across the depth of cobalt boride layer, obtained by both treatment conditions, were estimated using the depth-sensing Vickers microindentation test at a constant load. In addition, Vickers indentation fracture toughness tests were performed on the “pure zone” of the CoB layer (obtained by PPBP) considering a range of applied loads between 1.2 and 1.8 N, in contrast with the range of applied loads of 3–5 N performed in the cobalt boride layer obtained by the PPBP + DAP. Principally, the effect of the DAP resulted in a change of the microstructure of the cobalt boride layer and the modification of indentation properties; a distribution of compressive residual stresses was estimated along the depth of the cobalt boride layer, which drastically modified the fracture resistance to ~ 2.7 MPa m compared with a lower fracture value of ~ 0.5 MPa m obtained by the cobalt boride layer obtained by PPBP.

A correlation between fracture toughness and cohesion strength of molybdenum thermal sprayed coatings

The Molydenum thermal sprayed coatings on steel substrate using electric arc, atmospheric plasma spray and high velocity oxy-fuel spray were investigated. The tensile bond strength tests were made in order to examine the degree of adhesion/cohesion strength of coatings. The Vickers indentation fracture toughness tests were made on parallel and perpendicular direction to the coating-substrate interface in order to examine the fracture toughness of the material in relationship with the microstructure, indentation direction, hardness and the length of microcracks developed under different loads. It was found that the fracture toughness is influenced by the direction and load of indentation. It was established a correlation between the fracture toughness and cohesion strength of Mo coatings and a general trend was described

Microstructure and mechanical properties of Al-Cu joints diffusion-bonded with Ni or Ag interlayer

The heterogeneous joint constituted by Al and Cu were diffusion-bonded with Ni or Ag interlayer under different bonding parameters, which was compared with directly bonded Al-Cu joints to analyze the effects of the different intermetallic compounds (IMCs) produced at the joining interface on the joint mechanical properties. The joint microstructure was analyzed by scanning electron microscope (SEM), the compositions profiles across the joining interface were measured by energy dispersive spectroscopy (EDS), and the mechanical properties of joints were evaluated by hardness, indentation fracture toughness, and tensile test. The experiment results demonstrated that the Al-Ag-Cu and Al-Cu joints couldn't avoid the crack due to the thick, hard and brittle IMCs layer formed at the joining interface, while, the thickness of the IMCs in the Al-Ni-Cu joint is less than 3.8 μm, this thin IMCs layer ensured that the joining interface exhibited the lowest hardness and brittleness in microscales, so the Al-Ni-Cu joint was free of cracks not only after bonding but also under the load of indentation fracture toughness test. The tensile test indicated that the Al-Ni-Cu joint had the highest tensile strength (47 MPa), which was bonded with 50 μm thick Ni interlayer at 10 MPa, 520 °C, 60 min.

Novel graphene nanoplatelet reinforced 45S5 bioglass composites fabricated by Spark Plasma Sintering (SPS)

Event Abstract Back to Event Novel graphene nanoplatelet reinforced 45S5 bioglass composites fabricated by Spark Plasma Sintering (SPS) Zhong Li1*, Nay Win Khun1, Xiu-Zhi Tang1 and Khiam Aik Khor1 1 Nanyang Technological University, School of Mechanical & Aerospace Engineering, Singapore Introduction: The insufficient fracture toughness of 45S5 Bioglass® (45S5) constraints its extensive application as major load-bearing orthopedic implants[1],[2]. Satisfactory wear resistance is crucial for the in vivo fixation, integration and lifetime of 45S5-based prosthesis, but the tribological properties of bulk 45S5 are rarely reported[3],[4]. This study attempts to fabricate graphene nanoplatelet (GNP) toughened 45S5 composites by Spark Plasma Sintering (SPS) and investigate the effect of GNP addition on the composite’s wear properties. Materials and Methods: 45S5 powder was supplied by XL Sci-Tech Inc., US. Graphene oxide (GO) was synthesized using a modified Hummers method[5]. A colloidal process was utilized to obtain the GO/45S5 composite powders. The composites were sintered at 550°C for 3 min by an SPS system (Dr. Sinter 1050, SCM, Japan). In situ reduction of GO and enhancement of 45S5 matrix were simultaneously realized in this process. Sintered pellets with 0, 0.1, 0.5, and 1 wt.% GO added in the raw powder are denoted as BG0, BG0.1, BG0.5 and BG1, respectively. Samples were extensively characterized by SEM, TEM, Raman Spectroscopy, XRD, XPS, Nanoindentation, and Vickers indentation fracture toughness test[6]. Tribological properties were investigated by a ball-on-disk micro-tribological test (CSM High Temperature Tribometer, Switzerland) and surface profilometry. Results and Discussion: While the pristine 45S5 powder was amorphous, the sintered pellets were crystalline (Fig. 1a). Raman spectra shown in Fig. 1b prove that GNP survived the SPS process. The significantly decreased defect index ID/IG (intensity ratio of the D band and G band, values given in brackets) of sintered composites ("S" – sintered pellet, "P" – powder, and "W" – wear track) can be attributed to the restoration of sp2 bonds in the graphitic lattice[7]. Composite pellets showed lower Young’s modulus (E) and hardness (H) than BG0 (Fig 2a), possibly caused by more residual pores introduced by GNP addition. BG0.5 possessed the highest E and H among the three composites. All composite pellets showed higher fracture toughness (KIC) than BG0 (Fig. 2b). BG0.5 had the highest KIC of 1.22 MPa∙m1/2, corresponding to an exciting improvement of 130.2 % compared with BG0. Different toughening mechanisms, including crack deflection, crack bridging and sheet pull-out, can be clearly seen in Fig. 2c-f. BG0.5 showed the best wear resistance with the shallowest wear track (Fig. 3). Compared with BG0, its friction coefficient and specific wear rate were decreased by 21.3 % and 62.0 %, respectively, because of its improved KIC and the lubrication effect of GNP[8]. Wear resistance decreased from BG0.5 to BG1, possibly due to excessive GNP loading. The obviously increased ID/IG values after wear tests probably stem from new structural defects introduced by tearing off of graphene layers during repeated sliding. Conclusions: Novel GNP/45S5 nanocomposites were successfully fabricated through in situ GO reduction in SPS. The addition of 0.5 wt.% GO was proved to be the optimum which could improve KIC by 130.2 % and decrease friction coefficient and specific wear rate by 21.3 % and 62.0 %, respectively. The encouraging and exciting enhancement in both fracture toughness and wear resistance achieved in our study has opened new doors for broader application of 45S5 in bone tissue engineering. Z. Li thanks NTU for the University Research Scholarship

Microstructure and Mechanical Properties of TiAl<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> <i>in situ</i> Composite by Combustion Process

The microstructure and mechanical properties of TiAl3/Al2O3 in situ composite by combustion process are investigated in details. Pure Al powder and TiO2 powder were mechanically milled with a molar ratio of 13 : 3 at 300rpm for 18ks. This milling powder’s green compact coldpressed at 200MPa for 0.3ks sintered at 923 to 1173K for 1.8ks under Ar atmosphere. The microstructure of the sintered compact was identified by XRD, SEM and TEM/EDS. Mechanical properties were evaluated by Vickers hardness and indentation fracture toughness tests. The compacts at less than 973K consist of a TiAl3 phase and remained phases of Al and TiO2, while the compact at more than 1023K consist of TiAl3 matrix, dispersed Al2O3 particles and some plate like Ti3Al phase. The compacts at more than 1023K have the higher hardness around 800Hv compared to TiAl3 single phase compact with 450Hv. The fracture toughness of TiAl3/Al2O3 composite is about two times TiAl3 single phase compact. This improvement of hardness and toughness is attributed to the effect of the microstructure formation of dispersed Al2O3 particles and Ti3Al plate like phase in the TiAl3 matrix. [doi:10.2320/matertrans.Y-M2014823]

燃焼反応プロセスによるTiAl<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub>複合材料の微細組織と機械的性質

ABSTRACTThe microstructure and mechanical properties of TiAl3/Al2O3 in situ composite prepared via a combustion process were investigated in detail. Pure Al powder and TiO2 powder (molar ratio 13 : 3) were mechanically milled at 300 rpm for 18 ks. The milled powders were cold-pressed at 200 MPa for 0.3 ks and then green compact were sintered at 923 − 1173 K for 1.8 ks under Ar atmosphere. The microstructure of the sintered compact was analyzed using XRD, SEM and TEM/EDS, and the mechanical properties were evaluated using Vickers hardness and indentation fracture toughness tests. The compacts sintered at temperatures below 973 K consisted of a TiAl3 phase and remaining Al and TiO2 phases, while those sintered at temperatures above 1023 K consisted of a TiAl3 matrix, dispersed Al2O3 particles, and a plate-like Ti3Al phase. In addition, the compacts sintered above 1023 K had a higher hardness (approximately 800 Hv) compared to that of the TiAl3 single-phase compact (450 Hv). The fracture toughness of the TiAl3/Al2O3 composite was also approximately twice that of the TiAl3 single-phase compact. This improvement in the hardness and toughness is attributed to the microstructure of the composite, particularly the formation of dispersed Al2O3 particles and the Ti3Al plate-like phase in the TiAl3 matrix.

Mechanical properties and material removal characteristics of soft-brittle HgCdTe single crystals

Mechanical properties and material removal characteristics of mercury cadmium telluride (Hg0.84C0.16Te) single crystals were investigated by the use of indentation and single point diamond turning. The nanoindentation tests showed that the average values of elastic modulus and hardness were 40 and 0.55GPa, respectively. The fracture toughness estimated by Vickers indentation fracture toughness test was 0.200MPam1/2, in the predicted range of 0.204–0.235MPam1/2 by the Bifano model. The diamond turning experiments revealed that there was a threshold value in depth of cut that was responsible for the transition from ductile to brittle removal modes during the cutting of the Hg0.84C0.16Te single crystals. The measured critical depth of cut was between 1.5 and 2μm, in agreement with that of 1.541μm calculated by the Bifano model.

Mechanical Testing of Si<sub>3</sub>N<sub>4</sub>/SiC/Graphite Ceramic Composites

Pin-on-disc tribological tests were performed on Si3N4/SiC/graphite ceramic composites with 5N applied load, at room temperature in dry conditions. Tests were completed with microhardness tests (F=10N), indentation fracture toughness tests (F=100N), furthermore morphological analyses of the wear tracks by SEM. Based on SEM pictures of the wear traces the main damage mechanism could be identified as an abrasive wear. The purpose of the paper is to model the abrasive wear of the given composites. For this reason lateral crack chipping model suggested by Evans and Marshall for Si3N4 ceramics was used for the assessment of the worn volume of the abrasive wear process. The model has been applied with the aim of validating it

Evaluation of HVOF-sprayed WC–Co coatings for wood machining

A great concern to save the amount of tungsten carbide used in various mechanical components has become important because of an increase of global demand and the resultant sharp rise in the price in recent years. Sintered tungsten carbide (WC) tools are usually used in woodworking industry because of their excellent combination of hardness and toughness. However, the actual area necessary for cutting is very small compared to the overall cutting tool body. In this work, three high-velocity oxy-fuel (HVOF) sprayed WC–Co coatings with different carbide size (0.2, 2, and 6 µm) on high speed tool steel substrates were fabricated and then grinded to produce cutting tools. Characterization of the deposited coating was done by scanning electron microscope, X-ray diffraction, hardness and indentation fracture toughness tests. The wood machining tests were performed on natural wood (Apitong) and medium density fiberboard (MDF) to study their performance as a cutting tool. The results showed that the hardness values of the coatings were approximately the same as that of sintered material, while the fracture toughness values were significantly lower. The wood machining tests on Apitong revealed that the coating tools were worn by the same level of edge recession as the sintered material. However, they showed numerous edge chippings over the worn surfaces and the level of edge chipping tended to increase with reducing the carbide size. The wood machining tests on MDF revealed that the coating tools were worn by the same level of edge recession in the low density wear zone as the sintered material but by a significantly higher level in the high density wear zone.

硬質レジンを用いた３種破壊靭性試験法の比較

The aim of this study was to determine the adaptability of fracture toughness evaluation and the relationship between three testing methods: single-edge notched beam fracture toughness test (SENB), indentation fracture toughness test (IF), and notchless triangular prism fracture toughness test (NTP). Two types of indirect composite, Ceramage and Estenia C&B, were used. Four types of experimental specimens were prepared under two curing conditions for each composite resin. One curing condition was only light curing and the other was heat curing after light curing. The fracture toughness value (K(Ic)) of the experimental specimens was measured by each of the three fracture toughness tests. K(Ic) of each test was compared by ANOVA and Tukey's multiple comparison test for the adaptability of fracture toughness evaluation. Then the correlation of two tests was evaluated by a simple linear regression analysis. Evaluation of the load-strain curve (or load-deflection curve) and fracture surface observation of SEM suggested the plane strain fracture phenomenon. K(Ic) values obtained by the three testing methods were significantly different (p<0.01). SENB could separate significantly these experimental specimens into four groups. IF could separate them into two groups. NTP could separate them into three groups. The fracture toughness evaluation of NTP was almost the same as that of SENB. The relationship between SENB and NTP showed a significant correlation (R(2)=99.7%) and its equation was NTP (K(Ic))=0.82 SENB(K(Ic))+1.05. IF did not show a significant correlation. These indirect composites tested exhibited different fracture toughnesses. This difference occurred due to the contents and curing conditions. The adaptability of fracture toughness evaluation showed different values depending on the testing method. The relationship of SENB and NTP showed a significant correlation.

On the Vickers Indentation Fracture Toughness Test

The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the KIc of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre‐cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three‐dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an ill‐defined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests. Previously published fracture toughness results employing the VIF technique are reviewed. These reveal serious discrepancies in reported VIF fracture toughness values. Finally, recent fracture resistance measurements by the VIF technique for the Standard Reference Material SRM 2100 are presented. These are compared with standardized test results for the same material. It is concluded that the VIF technique is not reliable as a fracture toughness test for ceramics or for other brittle materials. What the VIF actually measures in terms of fracture resistance cannot be readily defined. It is recommended that the VIF technique no longer be acceptable for the fracture toughness testing of ceramic materials.

Local and Global Fracture Toughness of a Flame Sprayed Molybdenum Coating

This study deals with the failure of a flame sprayed molybdenum coating and its fracture mechanical characterization. The microstructure of the coating was examined by scanning electron microscopy. Local hardness and Young’s modulus values were measured by nanoindentation methods. X-ray measurements were used to estimate the grain size within the molybdenum splats. Special fracture mechanical tests were made to study the fracture mechanical behavior of cracks parallel and perpendicular to the coating-substrate interface. Indentation fracture toughness tests were made to examine the local fracture behavior of the material. Using these local toughness values and taking into account the microstructure, crack path, and mismatch effects it was possible to explain the global fracture toughness values.

Vickers indentation fracture toughness test Part 1 Review of literature and formulation of standardised indentation toughness equations

There is considerable interest in determining the fracture toughness of brittle materials by measuring the extent of cracking associated with a Vickers indentation because of the ease of specimen preparation and the simplicity of the test. However, confusion has been engendered by the multitude of models and equations in the literature relating the degree of cracking to the fracture toughness. In Part 1 of this work, nineteen of these equations are reviewed and then modified in a standard manner for both experimental convenience and direct comparison.MST/1050a

Vickers indentation fracture toughness test Part 1 Review of literature and formulation of standardised indentation toughness equations

There is considerable interest in determining the fracture toughness of brittle materials by measuring the extent of cracking associated with a Vickers indentation because of the ease of specimen preparation and the simplicity of the test. However, confusion has been engendered by the multitude of models and equations in the literature relating the degree of cracking to the fracture toughness. In Part 1 of this work, nineteen of these equations are reviewed and then modified in a standard manner for both experimental convenience and direct comparison.MST/1050a