Loss Of Toughness Research Articles

Property changes in thermo-hydro-mechanical processing

Abstract Thermo-hydro-mechanical (THM) treatment is a combined action of temperature, moisture, and mechanical force, which leads to modified wood (THMW). Various types of eco-friendly THM processes have been developed to enhance wood properties and generate new materials, such as welding, densification, molding, bending, profiling, artificial aging, panel manufacture, and surface densification. The various transformation processes in the course of THM bring about positive effects in terms of the mechanical and physical properties as well as the biological durability. To the negative effects belong the loss in strength and fracture toughness, and one of the challenges is to minimize these negative aspects. The present paper reviews the chemical transformations processes during THM treatment in a closed processing system and presents the relationship between processing parameters and THMW properties. The discussion includes the problems associated with eliminating the set recovery of densified wood by THM posttreatments and the chemical origin of the relaxation of internal stresses induced by densification.

Bone Material Properties and Skeletal Fragility.

Deformations of vertebrae and sudden fractures of long bones caused by essentially normal loading are a characteristic problem in osteoporosis. If the loading is normal, then the explanation for and prediction of unexpected bone failure lies in understanding the mechanical properties of the whole bone-which come from its internal and external geometry, the mechanical properties of the hard tissue, and from how well the tissue repairs damage. Modern QCT and MRI imaging systems can measure the geometry of the mineralized tissue quite well in vivo-leaving the mechanical properties of the hard tissue and the ability of bone to repair damage as important unknown factors in predicting fractures. This review explains which material properties must be measured to understand why some bones fail unexpectedly despite our current ability to determine bone geometry and bone mineral content in vivo. Examples of how to measure the important mechanical properties are presented along with some analysis of potential drawbacks of each method. Particular attention is given to methods useful to characterize the loss of bone toughness caused by mechanical fatigue, drug side effects, and damage to the bone matrix.

The Influence of Heat Treatment on the Microstructure and Machinability of a Prehardened Mold Steel

The machinability performance of a modified AISI P20 steel, heat treated to have the same hardness but three different microstructures, lower bainite, tempered martensite, and primary spheroidized carbides in a tempered martensite matrix, was studied. The microstructures were characterized using light optical and scanning electron microscopy and X-ray diffraction, and mechanical properties were compared by means of tensile and Charpy V-notch impact tests. The influence of microstructure and the resultant mechanical properties on machinability was studied in the context of single tooth end milling operation. The results showed that the material containing primary spheroidized carbides exhibited a superior machinability at the expense of a marginal loss of tensile strength and impact toughness, with comparable yield strength to that of the material containing tempered martensite. By contrast, the material with bainitic mi- crostructure showed the lowest yield strength and the poorest machinability performance while having the highest uniform elongation.

Bone micro-fragility caused by the mimetic aging processes in α-klotho deficient mice: In situ nanoindentation assessment of dilatational bands

The nanoscale structure-function relationship is a key determinant of bone toughness or micro-fragility. The loss of bone toughness during the aging process has been accepted based on empirical evidence, but this concept has not yet been fully supported by evidence at the material level. Here, we demonstrate a reduction in bone toughening mechanism in mimetic aged cortical bone obtained from α-klotho deficient (α-klotho−/−) mice and assessed by in situ dynamic mechanical analysis. The strain-rate nanoindentation tests showed enhanced stiffening of the wild-type calvarial bone and a large dimensional recovery during rapid loading following the constant displacement test. Such strain-dependent stiffening was likely associated with nanoscale dilatational bands and subsequent strain-energy transfer to the superior wild-type cross-linked collagen matrix network. The absence of dilatational bands formed by hydroxyapatite crystals and non-collagenous proteins in the α-klotho−/− bone samples likely diminished the intrinsic bone toughening mechanisms almost independent of viscoelastic behaviors. Such nanoscale structural alternations that occur during aging processes lead to crack propagation and result in overall bone fractures under large external stresses. In addition, dynamic mechanical analysis using instrumented nanoindentation was useful for the evaluation of bone mechanical properties in this pathological model of a genetic knockout mouse.

Effect of welding parameters on mechanical properties of GTAW of UNS S31803 and UNS S32750 weldments

Duplex Stainless Steel (DSS) and Super Duplex Stainless Steel (SDSS) pipes were welded by Gas Tungsten Arc Welding (GTAW) process. The effect of welding parameters such as heat input, cooling rate, shielding/purging gas composition and interpass temperature on tensile strength, hardness and impact toughness were studied. The microstructure analysis revealed presence of intermetallic phases at root region of the weldments. All mechanical properties were improved at lower heat input and high cooling rate due to grain refinement and balanced microstructure [ferrite and austenite]. All weldments exhibited higher strength than base materials. Weld root region was harder than centre and cap region. SDSS is more susceptible to sigma phase formation due to higher alloying elements and weld thermal cycles, which lead to considerable loss of toughness. Higher nitrogen contents in shielding and purging gas resulted strengthening of austenite phase and restriction of dislocations, which ultimately improved mechanical properties. Higher interpass temperature caused reduction in strength and toughness because of grain coarsening and secondary phase precipitation.

Strength and ductility optimization of Mg–Y–Nd–Zr alloy by microstructural design

Understanding of essential microstructural features necessary to develop an optimum combination of strength and ductility in magnesium alloys is needed for materials by the microstructural design approach. Microstructural features required to optimize both strength and ductility of Mg–Y–Nd–Zr alloy were investigated by examining different thermo-mechanical processing conditions. Different microstructural states were obtained by either isothermally aging the hot-rolled base alloy or by friction stir processing (FSP) the base alloy and then aging the FSP microstructure. The plastic deformation behavior of different microstructural states was characterized by uniaxial tensile testing, whereas microstructural features were probed using scanning electron microscope, electron backscatter diffraction, and transmission electron microscope. As expected, precipitate formation within α-Mg matrix increased the alloy strength irrespective of processing condition. Concomitantly, the base alloy experienced a drastic drop in ductility. The presence of twins, coupled with a loss of toughness due to aging heat treatment, resulted in very poor ductility of the alloy. A good combination of strength and ductility was achieved by altering the base Mg–Y–Nd–Zr microstructure through FSP and subsequent aging. In addition to producing refined grains, FSP resulted in twin-free microstructure. The refined microstructure had a near-random texture, where a large fraction of grains was favorably oriented for plastic deformation. In this condition, intragranular precipitation increased the strength while retaining good ductility by activating additional slip systems. These results indicate that an optimum balance of strength and ductility is achieved by engineering a microstructure containing randomly-oriented fine grains, intragranular precipitation and minimal twins within α-Mg matrix. An empirical correlation among ductility, work hardening exponent, and slope of work hardening vs. flow stress curve was established, and will serve as a useful guideline for designing microstructure for the optimization of strength and ductility in magnesium alloys.

Study of cracking process of clay cap barrier in landfill using X-ray CT

In Japan, surface facilities are being considered, as is already the case in France, for the storage of low-activity nuclear wastes. At these sites, a compacted clay liner (CCL) in combination with different soil and geosynthetic layers is generally used as a cap barrier. The aim of the CCL is to limit the infiltration of moisture, especially that due to rainfall, through the barrier into the waste body and to inhibit the possible release of radon gas into the atmosphere. However, the cap cover may be subjected to differential settlement that could induce cracking and consequently cause loss of fluid toughness, namely; greenhouse gas emission. Indirect tensile tests, such as punching and bending tests, are carried out on the CCL to characterize its sensitivity to cracking. In this study, a method based on the use of an X-ray CT scanner is presented for determining the deformation field of the specimen. This paper first describes the X-ray CT scanner and then discusses the improved facility developed for the new device used for the bending test. It is demonstrated that this method is suitable for determining the evolution of cracking in the clay specimen. To improve the observation accuracy of the CCL due to loading, a bending apparatus is newly developed for an X-ray CT scanner. This allows the inner conditions of CCL, especially cracks, due to loading to be observed and evaluated with little disruption of the specimen behavior.

Influence of Welding Wire Selection on the Strength and Toughness of Welded Armor Steel Joints*

Abstract Since MIL-A-46100D high hardness armor steel plates with excellent resistance to penetration exhibit high strength, selecting the proper electrode used in the gas metal arc welding process is particularly important to obtain a weld joint with high quality satisfying the adequate strength and toughness requirements at the same time. Selecting a consumable electrode with a lower strength than the armor material enhances the ductility and the toughness, reduces the risk of cracking in the weld zone, but it may lead to a considerable loss in strength of welded armor steel joints as well. Thus, an optimization of strength and toughness is required in welding high hardness armor steel plates. Within the scope of this study, two different austenitic stainless solid wires, one of which conforms to AWS 5.9 and the other one to AWS 5.28, and two different cored wires conforming to AWS 5.29 standards were analyzed and compared with respect to weld joint strength and toughness. Although weld joints fabricated with solid wires were superior in weld toughness, weld joints with austenitic cored wires exhibited considerably higher tensile strengths without a significant loss in toughness.

Thermal shock behavior of platinum aluminide bond coat/electron beam-physical vapor deposited thermal barrier coatings

Thermal barrier coating systems (TBCs) including of chemical vapor deposited (Ni, Pt)Al bond coat with grit blasting process and electron beam physical vapor deposited Y2O3-stabilized-ZrO2 (YSZ) ceramic coating were investigated. The phase structures, surface and cross-sectional morphologies, thermal shock behaviors and residual stresses of the coatings were studied in detail. Grain boundary ridges still remain on the surface of bond coat prior to the deposition of the ceramic coating, which are shown to be the major sites for spallation damage initiation in TBCs. When these ridges are mostly removed, they appear some of cavities formation and then the damage initiation mode is deteriorated. Damage initiation and progression occurs at the bond coat to thermally grown oxide (TGO) interface leading to a buckling failure behavior. A buckle failure once started may be arrested when it runs into a region of high bond coat to TGO interface toughness. Thus, complete failure requires further loss in toughness of the bond coat to TGO interface during cooling. The suppressed cavities formation, the removed ridges at the grain boundaries, the relative high TGO to bond coat interface toughness, the uniform growth behavior of TGO thickening and the lower of the residual stress are the primary factors for prolonging the lifetime of TBCs.

Natural polyphenols enhance stability of crosslinked UHMWPE for joint implants.

Radiation-crosslinked UHMWPE has been used for joint implants since the 1990s. Postirradiation remelting enhances oxidative stability, but with some loss in strength and toughness. Vitamin E-stabilized crosslinked UHMWPE has shown improved strength and stability as compared with irradiated and remelted UHMWPE. With more active phenolic hydroxyl groups, natural polyphenols are widely used in the food and pharmaceutical industries as potent stabilizers and could be useful for oxidative stability in crosslinked UHMWPE. We asked whether UHMWPE blended with polyphenols would (1) show higher oxidation resistance after radiation crosslinking; (2) preserve the mechanical properties of UHMWPE after accelerated aging; and (3) alter the wear resistance of radiation-crosslinked UHMWPE. The polyphenols, gallic acid and dodecyl gallate, were blended with medical-grade UHMWPE followed by consolidation and electron beam irradiation at 100 kGy. Radiation-crosslinked virgin and vitamin E-blended UHMWPEs were used as reference materials. The UHMWPEs were aged at 120 °C in air with oxidation levels analyzed by infrared spectroscopy. Tensile (n = 5 per group) and impact (n = 3 per group) properties before and after aging as per ASTM F2003 were evaluated. The wear rates were examined by pin-on-disc testing (n = 3 per group). The data were reported as mean ± SDs. Statistical analysis was performed by using Student's t-test for a two-tailed distribution with unequal variance for tensile and impact data obtained with n ≥ 3. A significant difference is defined with p < 0.05. The oxidation induction time of 100 kGy UHMWPE was prolonged to 144 hours with 0.05 wt% dodecyl gallate and 192 hours with 0.05 wt% gallic acid compared with 48 hours for 0.05 wt% vitamin E-blended UHMWPE. Accelerated aging of these polyphenol-blended UHMWPEs resulted in ultimate tensile strength of 50.4 ± 1.4 MPa and impact strength of 53 ± 5 kJ/m(2) for 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate, for example, in comparison to 51.2 ± 0.7 MPa (p = 0.75) and 58 ± 5 kJ/m(2) (p = 0.29) before aging. The pin-on-disc wear rates of 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate and 0.05 wt% gallic acid were 2.29 ± 0.31 and 1.65 ± 0.32 mg/million cycles, comparable to 1.68 ± 0.25 and 2.05 ± 0.22 mg/million cycles for 100 kGy-irradiated virgin and 0.05 wt% vitamin E-blended UHMWPE. Based on the sample numbers tested in this study, polyphenols appear to effectively enhance the oxidation stability without altering the mechanical properties or pin-on-disc wear rate of radiation-crosslinked UHMWPE. Crosslinked UHMWPE with natural polyphenols with improved oxidative stability and low wear may find clinical application in joint implants.

The effect of alkali–silica reaction on strength and ductility analyses of RC beams

Alkali–silica reaction (ASR) causes an increase in concrete volume and results in its failure. The effect of ASR on the strength, ductility and deformability of reinforced concrete (RC) beams under sustained load was investigated in this research. In total, 12 reinforced beam specimens, six with reactive aggregate (R beams) and six with non-reactive aggregate (N beams), were loaded and kept in a suitable environment for 360 d. Flexural loading tests were then carried out and the attributed deflections subsequently analysed with respect to total applied load to check the strength, stiffness, reinforcement yielding load and the ultimate load of the specimens due to ASR. Ductility and deformability analyses were conducted using related parameters. The experimental results indicate that ASR has a considerable effect on the R beams (where cracks occurred at lower loads) and, in the condition of loading up to ultimate load, the N beams were stronger than their equivalent R beams. Likewise, in R beams under load, there was a loss of toughness owing to loss of flexural stiffness. It was also found that, for both compression steel and a higher ratio of tension steel in the beams, the flexural behaviour of R beams and N beams will be quite similar. Furthermore, despite losses in the ductility of most of the R beams, failure of these beams was ductile with sufficient warning.

Application of low Ms temperature consumable to dissimilar welded joint

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe–Cr–Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with Ms temperature below 200°C and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.

Microstructure and mechanical properties of two Api steels for iron ore pipelines

This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present.

Damask Steel – Unalloyed Carbide Class Steel

Once, the question was posed: “What is damask steel – special steel or technology?” and I could not answer. Everything is simple and simultaneously complicated. People have used damask steel for a thousand years. Legends are made up about it. Today secrets of the microworld are being opened up, but damask steel microstructure, determining its properties, has remained in the shade of its reputation. However, only composition and structure govern steel properties. Any steel is prepared by specific technology. There is technology for preparing die steels (X12), and there is technology for preparing high-speed steels (R18), and consequently there should also be technology for preparing damask steel. As a result of searching for technology for preparing damask steel it has become known that for the very best damask steels the amount of carbon within their composition approaches that of cast iron. With high-temperature treatment of these alloys there is a risk of forming free graphite, as a result of which there is inevitable loss of toughness. A condition for forming graphite is the presence of crystallization centers (silicon compounds). Composition purity is a starting factor for revealing the main structural components governing damask steel properties. So, in order to understand today why blade sharpness is combined with high elasticity it is necessary to reveal the true structure of damask steel and to establish the underlying features of its individual properties. Experimental study of the structure makes it possible to determine what all of them are in the field of unalloyed carbide class steels.

Low‐temperature ductility and structural behaviour of cold‐formed hollow section structures – progress during the past two decades

AbstractCold‐formed hollow sections are a widely used tubular construction material. The applicability, weldability and reliability of cold‐formed rectangular hollow sections are sometimes questioned because of the consequences of cold forming and inhomogeneous cross‐sections. One of the main concerns is related to the cold‐formed corner areas and possible loss of toughness due to strain ageing in the vicinity of the welds. Conventional hot‐rolled C‐Mn steels are susceptible to strain ageing, and Eurocode 3 includes restrictions on welding in the cold‐formed corner area. Both steelmaking and hot rolling have undergone crucial developments and this has had an impact on cold‐formed hollow sections. Thermomechanically rolled fine‐grain steels became state of the art at the end of the 1990s. This study confirms that cold‐formed EN 10219 hollow sections made of suitable fine‐grain steels have a similar Charpy‐V toughness on the flat face and in the corner, and that even after ageing the transition temperature T40J in the corner area is at a very low level, typically below –50 °C. The load and deformation capacities of X‐ and K‐joints fulfil the requirements without any noticeable ageing effects. The advances in steelmaking and hot rolling enable the manufacturing of reliable and versatile cold‐formed EN 10219 hollow sections for welded structures with good low‐temperature ductility even in the cold‐formed corner area.

Multiscale thermodynamic analysis on fracture toughness loss induced by solute segregation in steel

A significant loss of fracture toughness () is induced by intergranular (grain boundary; GB) segregation of metalloid solute in alloy steels. Yet, the mechanism has not been clarified from a multiscale point of view. From a thermodynamic approach aided by first-principles calculations, it is shown that segregated solute with higher energetic stability on fracture surfaces causes a larger linear reduction in the ideal work to intergranular fracture (); i.e. the energy difference between a GB and its two fracture surfaces. Remarkably, the combined analysis with first-principles calculations and fracture mechanics experiments found several orders of magnitude more energy loss in for a specific range in the within only a few tenths of . These results illustrate that the GB of steel has the threshold energy of atomic cohesion under which catastrophic failure occurs. Our research scheme would play a key role in identifying specific solute elements to toughen the GB in metallic systems used under aggressive environments.

Fracture resistance of human cortical bone across multiple length-scales at physiological strain rates

While most fracture-mechanics investigations on bone have been performed at low strain rates, physiological fractures invariably occur at higher loading rates. Here, at strain rates from 10−5 to 10−1 s−1, we investigate deformation and fracture in bone at small length-scales using in situ small-angle x-ray scattering (SAXS) to study deformation in the mineralized collagen fibrils and at the microstructural level via fracture-mechanics experiments to study toughening mechanisms generating toughness through crack-tip shielding. Our results show diminished bone toughness at increasing strain rates as cracks penetrate through the osteons at higher strain rates instead of deflecting at the cement lines, which is a prime toughening mechanism in bone at low strain rates. The absence of crack deflection mechanisms at higher strain rates is consistent with lower intrinsic bone matrix toughness. In the SAXS experiments, higher fibrillar strains at higher strain rates suggest less inelastic deformation and thus support a lower intrinsic toughness. The increased incidence of fracture induced by high strain rates can be associated with a loss in toughness in the matrix caused by a strain rate induced stiffening of the fibril ductility, i.e., a “locking-up” of the viscous sliding and sacrificial bonding mechanisms, which are the origin of inelastic deformation (and toughness) in bone at small length-scales.

Mechanical and metallurgical characterisation of electroformed nickel for helicopter erosion shield applications

The influence heat treatment has on the tensile, notch toughness, microstructure and fatigue properties of electroformed nickel have been studied. From the test data it is clear that by exposing electroformed nickel to temperatures in excess of 250°C a significant loss of tensile strength, ductility and notch toughness occurs. In addition stiffness has been shown to gradually increase when exposed to temperatures from 200°C onwards. The change in properties appears to be associated with microstructural changes, i.e. the crystallite structure is thermally unstable and gradually recrystallizes leading to breakdown of the fine crystallites and subsequent grain growth. In the case of ductility the severe reduction is considered to be primarily due to embrittlement caused by sulphur within the electroform precipitating out around the grain and sub-grain boundaries. Consequently, for electroformed nickel to be considered an engineering material for erosion shield applications it should not be subjected to temperatures above 200°C.Based on erosion shield cut ups, electroformed nickel appears to be essentially isotropic in nature due in part to the extremely fine crystalline microstructure. As mechanical property variability is greater with electroformed nickel when compared to wrought products it is essential that integral mechanical property test pieces are employed in order to be able to fully characterise the properties within the electroform. Certain electroforming defects have been shown to lower high cycle fatigue life; hence it is vitally important that in case of critical components, robust Non-Destructive Inspection (NDI) techniques are employed to ensure they are eliminated from production components.

Structure–property relationships in nylon 6 nanocomposites based on octaphenyl‐, dodecaphenyl–POSS, montmorillonite, and their combinations

Binary and ternary nanocomposites were produced by incorporating, via melt compounding, two types of octa‐ and dodecaphenyl substituted polyhedral oligomeric silsesquioxanes (POSS), montmorillonite (MMT), and combinations of POSS with MMT into nylon 6. The tensile, flexural, and dynamic thermo‐mechanical properties of these materials were characterized and their structure–property relationships discussed. The results show that the losses in ductility and toughness experienced after inclusion of MMT into nylon 6 can be balanced out by co‐mixing MMT with the dodecaphenyl–POSS to produce a ternary nanocomposite. This trend however was less pronounced in the ternary MMT/octaphenyl–POSS system. Analysis of the microstructure organization in these materials using XRD and SEM sheds some light on understanding the differences in behavior. Both types of POSS particles mixed alone in nylon 6 were found to be polydisperse (500 nm to a few microns in size) and locally aggregated, yielding materials with similar mechanical performance. The co‐mixing of MMT with the octaphenyl–POSS served to break down the POSS crystal aggregates, enhancing their micro‐mechanical reinforcing action. On the other hand, the POSS crystals were not affected in the MMT/dodecaphenyl–POSS system, which led to improving their toughening ability. POLYM. COMPOS., 36:153–160, 2015. © 2014 Society of Plastics Engineers

Effects of doping CeO2/TiO2 on structure and properties of silicate glass

In order to elucidate the effects of doping CeO2/TiO2 on the structure and physical properties of silicate glass, glasses with composition 72SiO2–3Al2O3–10Na2O–10K2O–5CaO doped with varied ratios of CeO2/TiO2 were synthesized by melt-quenching method and were characterized by X-ray diffraction, infrared and Raman spectrometry, UV–Visible spectrophotometry and micro-indentations. X-ray diffraction conforms the amorphous state of doped glasses. The spectroscopic analysis reveals that doping CeO2 alone results in depolymerization of glass network and narrowed distribution of Qn (Si–O tetrahedral with n bridging oxygen atoms), while doping TiO2 singly or combined with CeO2 favors the enhanced polymerization of network and regains a broader Qn distribution relative to doping CeO2 alone. It is proposed that doped cerium and titanium in glass exists in multivalent state and the former in presence of trivalent state preferentially acts as modifier inducing network depolymerization, whilst the latter in form of tetrahedral tends to interconnect network units as intermediate. Doped cerium in trivalent state contributes mainly to the red-shift of absorption edge while titanium suppresses such change of absorption band. Either adding cerium alone or co-doping with titanium will result in decreased optical band gap due to the structural modifications. The relatively loosened structure due to depolymerization induced by cerium is responsible for the decline in hardness and E-modulus but rising in fracture toughness, whereas network compactness by virtue of interconnectivity of titanium and structural densification may account for the increase of hardness and E-modulus at the cost of slight loss of fracture toughness. For silicate glasses co-doped cerium and titanium, the mechanical properties should be the synergy of the two opposite mechanism.