Creep rupture life prediction of high-temperature titanium alloy using cross-material transfer learning

High-temperature titanium alloys are the key materials for the components in aerospace and their service life depends largely on creep deformation-induced failure.However,the prediction of creep rupture life remains a challenge due to the lack of available data with well-characterized target property.Here,we proposed two cross-materials transfer learning(TL)strategies to improve the prediction of creep rupture life of high-temperature titanium alloys.Both strategies effectively utilized the knowledge or information encoded in the large dataset(753 samples)of Fe-base,Ni-base,and Co-base superalloys to enhance the surrogate model for small dataset(88 samples)of high-temperature titanium alloys.The first strategy transferred the parameters of the convolutional neural network while the second strategy fused the two datasets.The performances of the TL models were demonstrated on different test datasets with varying sizes outside the training dataset.Our TL models improved the predictions greatly compared to the mod-els obtained by straightly applying five commonly employed algorithms on high-temperature titanium alloys.This work may stimulate the use of TL-based models to accurately predict the service properties of structural materials where the available data is small and sparse.

Experimental analysis of HR-120 alloy used for high-temperature fans

High-temperature circulating fans blow 800 ℃ HN protective atmosphere to the surface of the strip as a jet heating power source or suspending source,playing a core role in metal strip continuous annealing furnaces. In this study,several high-temperature alloys were experimentally compared based on their high-temperature mechanical properties,high-temperature creep resistance,and high-temperature oxidation resistance. The results indicate that though the price of HR-120 alloy is only half of Inconel 601,it is suitable for the manufacture of fans that can withstand a high temperature of 800 ℃ given its good creep resistance,high-temperature oxidation resistance,and price advantage.

On-Line Life Monitoring Technique for Tube Bundles of Boiler High-Temperature Heating Surface

High-temperature heating surface such as superheater and reheater of large-sized utility boiler all experiences a relatively severe working conditions. The failure of boiler tubes will directly impact the safe and economic operation of boiler. An on-line life monitoring model of high-temperature heating surface was set up according to the well-known L-M formula of the creep damages. The tube wall metal temperature and working stress was measured by on-line monitoring, and with this model, the real-time calculation of the life expenditure of the heating surface tube bundles were realized. Based on the technique the on-line life monitoring and management system of high-temperature heating surface was developed for a 300 MW utility boiler. An effective device was thus suggested for the implementation of the safe operation and the condition-based maintenance of utility boilers.

A multifunctional shear apparatus for rocks subjected to true triaxial stress and high temperature in real-time

Deep engineering disasters,such as rockbursts and collapses,are more related to the shear slip of rock joints.A novel multifunctional device was developed to study the shear failure mechanism in rocks.Using this device,the complete shearedeformation process and long-term shear creep tests could be performed on rocks under constant normal stiffness(CNS)or constant normal loading(CNL)conditions in real-time at high temperature and true-triaxial stress.During the research and development process,five key technologies were successfully broken through:(1)the ability to perform true-triaxial compressioneshear loading tests on rock samples with high stiffness;(2)a shear box with ultra-low friction throughout the entire stress space of the rock sample during loading;(3)a control system capable of maintaining high stress for a long time and responding rapidly to the brittle fracture of a rock sample as well;(4)a refined ability to measure the volumetric deformation of rock samples subjected to true triaxial shearing;and(5)a heating system capable of maintaining uniform heating of the rock sample over a long time.By developing these technologies,loading under high true triaxial stress conditions was realized.The apparatus has a maximum normal stiffness of 1000 GPa/m and a maximum operating temperature of 300C.The differences in the surface temperature of the sample are constant to within5C.Five types of true triaxial shear tests were conducted on homogeneous sandstone to verify that the apparatus has good performance and reliability.The results show that temperature,lateral stress,normal stress and time influence the shear deformation,failure mode and strength of the sandstone.The novel apparatus can be reliably used to conduct true-triaxial shear tests on rocks subjected to high temperatures and stress.

CREEP BEHAVIORS OF Pt-RE ALLOYS AT HIGH TEMPERATURES

The creep behaviors of Pt-RE alloys have been studied at 1200℃ and 1400℃.The results show that asmall amount of RE elements improves the creep behaviors of platinum greatly.The creep behaviors of PtGd0.5,PtLa0.5 and PtLa0.3 Gd0.2,are best among all the alloys studied.As far as the creep behaviors are concerned,the traditional heat-resistance alloy PtGd10 can be replaced by PtGd0.5.Particularly,the properities of PtGd0.5are near to those of PtRb10.For most of the Pt-RE alloys,long-time,static,super high-temperature treatment inair is of no advantage to the creep rupture life.The mechanisms of the effects of rare-earths on high-temperaturecreep properties of platinum are discussed.

COMPARISON OF FATIGUE AND CREEP BEHAVIOR BETWEEN 2D AND 3D-C/SiC COMPOSITES

The differences of tension-tension fatigue and tensile creep characters of 2D-C/SiC and 3D-C/SiC composites have been scrutinized to meet the engineering needs. Experiments of tension-tension fatigue and tensile creep are carried out under vacuum high temperature condition. All of the high temperature fatigue curves are flat; the fatigue curves of the 2D-C/SiC are flatter and even parallel to the horizontal axis. While the tension-tension fatigue limit of the 3D-C/SiC is higher than that of the 2D-C/SiC, the fiber pullout length of the fatigue fracture surface of the 3D-C/SiC is longer than that of the 2D-C/SiC, and fracture morphology of the 3D-C/SiC is rougher, and pullout length of the fiber tows is longer. At the same time the 3D-C/SiC has higher tensile creep resistance. The tensile curve and the tensile creep curve of both materials consist of a series of flat step. These phenomena can be explained by the non-continuity of the damage.

Creep Behaviour of Fe-Mn Binary Alloys

Tensile creep behaviour of fine-grained Fe-Mn binary alloys containing 0.42-1.21 wt. % Mn has been investigated in the temperature range from room temperature to 475K under 10-50 MPa. Tensile tests are carried out with a constant cross-head speed under uniaxial load at a strain rate 10^-4s^-1. Stress exponent and activation energy are determined to clarify deformation mechanism. The obtained variation of steady state creep rate with respect to the applied stress for Fe-Mn binary alloys exhibits two distinct regimes at about 20 MPa, indicating a possible change in creep mechanism. The average stress exponent is approximately 2.2, which is a characteristic of grain boundary sliding in the alloys. The activation energy for plastic flow varies from 135 to 92k J/mol, depending on the Mn content.

Influence of Temperatures on Creep Behavior of Pt-Al Coated Third-Generation Low-Cost Single Crystal Superalloy

The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal(SX)superalloy with Pt-Al coating was evaluated.The creep damage was observed under the conditions of 1100℃/137 MPa,1120℃/137 MPa,and 1140℃/137 MPa.Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions.The most significant reduction in creep life reaches 50%when the test condition is 1100℃/137 MPa.At higher temperatures(1120 and 1140℃),the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases,thereby reducing the degradation degree of mechanical properties.Instead of the penetration into SX substrate,tip oxidation and Al diffusion of the coating cracks cause the formation of oxides,therefore leading to the slow degradation in microstructures of the substrate beneath the coating.At 1100℃,however,the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion.This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100℃.At 1120 and 1140℃,the dislocation of SX superalloy substrate beneath the coating is relatively unchanged,compared to that in the inner superalloy.In contrast,the dislocation network of the substrate beneath the coating becomes sparse,and the number of superdislocations cutting intoγ′phases increases at 1100℃.

Rheological Regime of the Upper Mantle beneath the Taiwan Strait and Its Tectonic Significance

This paper deals with deformation textures and fabrics of mantle-derived xenoliths and dislocation microstructures of olivine in the upper mantle in the Penghu Islands, Taiwan. According to the calculation of the chemical composition of xenolith minerals (pyroxene), the equilibrium temperatures and pressures were 986-1116@ and 1.50-2.60 GPa, respectively. Deformation events in the upper mantle may fall into three sequences' (1) uniform steady-state flow deformation with high temperatures and low stresses, (2) shear flow deformation with high temperatures and relatively high stresses on diapiric margins of the upper mantle, and (3) extraction deformation of {110} glide bands with low temperatures and high strain rates. Deformation events and thermal structure of the upper mantle in the study area show that eastern Fujian and the Penghu Islands are characterized by very similar rheological properties of the upper mantle. Volcanism of basalts in the Penghu Islands is related to hot spots of the upper mantle under neath the Taiwan Strait, and diapirism and upwelling of the upper mantle are the dominant factors responsible for rifting of the continental margins in eastern China.

MECHANICAL PROPERTIES OF Ti_3SiC_2 AT HIGH TEMPERATURE

Creep and stress relaxation behavior, the elastic modulus and fracture toughness of machinable Ti3SiC2 at various temperatures from 20 to 1250℃ were investigated by means of three-point bending tests. The experiments were performed respectively at: (i) fixed stress and changed temperatures, and (ii) fixed temperature and changed stresses. A creep resistance parameter that represents the probability of creep deformation in a given condition was defined as a function of both applied stress and the threshold stress, varying in a range from 0 to 1. Elastic modulus at high temperatures was measured through comparing relative slopes of loading curves in cyclic loading curve. The fracture toughness measured by SENB method showed a stable value in the range of 25-1000℃, but over 1000℃, it declined abruptly from -6.7MPa·m1/2 to -2.0MPa·m1/2 at 1200℃.

An overview on the novel heat-resistant ferritic stainless steels

Heat-resistant ferritic stainless steels are widely used in many high-temperature applications such as power plants,automotive exhaust manifolds and solid oxide fuel cell interconnects due to their low price,low coefficient of thermal expansion,high thermal conductivity,high thermal fatigue resistance,high creep performance and excellent corrosion resistance.High-temperature strength,formability,high-temperature oxidation resistance and creep performance are the main evaluation criteria for the application.With the development of relevant industries,higher requirements are proposed for the performance of ferritic stainless steels.Therefore,the development of a new generation of heat-resistant ferritic stainless steel has received extensive attention.In this presentation,we summarized the research progress of heat-resistant ferritic stainless steels including high-temperature strength,formability,high-temperature oxidation resistance and creep performance.Meanwhile,some suggestions are given for alloy composition design and microstructure optimization.The future research direction of heat-resistant ferritic stainless steels also prospected.