Weld deformation control based on programmable multi-point flexible support

T-joint titanium alloy structures are commonly used in aircraft manufacturing, and their laser welding process is relatively mature, but due to the strict requirements of the airplane production, the angular deformation caused by uneven heat input across the sheet is still not negligible, so active control needs to be imposed. In this paper, an active deformation control method based on programmable multipoint flexible support is proposed and validated. In response to the problem that the tradit...     

R & D ACTIVITIES ON AEROSPACE MATERIALS IN KOREA

This paper briefly reviews research and development programs in Korean aerospace industry,with an emphasis on aircraft materials technology. International collaborations in these areas are outlined and the R & D activities are highlighted against the　background of the national economy.It is shown that the investment from government agencies and large enterprises has led to healthy development of aerospace materials industries in Korea.     

Laser surface hardening of gray cast iron used for piston ring

The process parameters for laser surface-hardening has been experimentally established for improving the wear life of piston rings used for marine diesel engines by the formation of a proper hardened layer on it. The parameters of interest were the laser power and travel speed. Various hardened layers of gray cast iron were analyzed with respect to microstructure, hardness value, hardening depth, surface roughness, and wear resistance. The hardness of the laser-hardened layer was in a range between 840 and 950 Hv0.1, regardless of the laser power and travel speed range studied. Both the surface roughness and hardening depth increased in an almost linear manner with the increase in the heat input applied. Thus, the hardened layers formed with heat input ranges between 30 and 45 J/mm satisfied the piston ring application requirements for surface roughness (<6.3 μm in Ra) and the minimum effective hardening depth of 0.3 mm (>450 in Vickers number). Wear-test results obtained using a pin-on-disk-type wear-test machine showed that the wear life of the laser-hardened layer was almost twice that of the untreated one. This was directly attributed to the formation of the martensitic microstructure.     

Determination of strain criterion of Portevin-Le Chatelier effect for aluminum alloy sheets

According to the deformation state in skin stretch forming, an experiment was investigated to determine the critical strain, which make the slip line occur, and the strain criteria under different strain paths are obtained. The uniaxial tension tests of different specimens were carried out to determine the critical strains of different strain paths. Then, the slip line limited curve（SLC） is available from these critical strains. Two kinds of aluminum alloys, 2024-T3 and 2524-T3, were studied, and two SLCs are gained. The application of the SLC to an airplane skin stretch forming simulation was investigated, and the results show that the SLC can be used to control the slip lines occurring in practice.     

Accelerated corrosion test and corrosion failure distribution model of aircraft structural aluminum alloy

Based on corrosion damage data of 1 0 years for a type of aircraft aluminum alloy, the statistical analysis was conducted by Gumbel, Normal and two parameters Weibull distribution function. The results show that aluminum alloy structural member has the corrosion history of pitting corrosion--intergranular corrosion-exfoliation corrosion, and the maximum corrosion depth is in conformity to normal distribution. The accelerated corrosion test was carried out with the complied equivalent airport accelerated environment spectrum. The corrosion damage failure modes of aluminum alloy structural member indicate that the period of validity of the former protective coating is about 2.5 to 3 years, and that of the novel protective coating is about 4.0 to 4.5 years. The corrosion kinetics law of aluminum spar flange was established by fitting corrosion damage test data. The law indicates two apparent corrosion stages of high strength aluminum alloy section material： pitting corrosion and intergranular corrosion/exfoliation corrosion. The test results agree with the statistical fit result of corrosion data collected from corrosion member in service. The fractional error is 5.8% at the same calendar year. The accelerated corrosion test validates the corrosion kinetics law of aircraft aluminum alloy in service.     

Optimization on springback reduction in cold stretch forming of titanium-alloy aircraft skin

An optimization method was presented for cold stretch forming of titanium-alloy aircraft skin to determine process parameters and to reduce springback.In the optimization model,a mathematical formulation of stress difference was developed as an indicator of the degree of springback instead of implicit springback analysis.Explicit finite element method(FEM)was used to analyze the forming process and to provide the stress distribution for calculating the amount of the stress indicator.In addition,multi-island genetic algorithm(MGA)was employed to seek the optimal loading condition.A case study was performed to demonstrate the potential of the suggested method.The results show that the optimization design of process parameters effectively reduces the amount of springback and improves the part shape accuracy.It provides a guideline for controlling springback in stretch forming of aircraft skin.     

FATIGUE BEHAVIOUR OF SiC_p/6061Al COMPOSITE

The fatigue of SiC_p/6061Al composite containing 15 v.-% SiC particles has been compared with 6061Al alloy.Dislocation structure and microprocess of fatigue crack initiation and propagation in the composite have been investigated by using SEM and TEM.The results in- dicate that the fatigue strength at 10~7 cycles of the composite is 196 MPa,i.e.about 25% higher than matrix alloy.The voids and microcracks initiated at and near the interface be- tween SiC_p and matrix,where has a higher density of dislocations,will propagate and link up to form the fatigue crack.It is an important evidence to note that the dislocation channels where screw dislocation can travel are formed near interface and corner region of SiC_o in the composite subjected to fatigue stress(σ_(max)=274 MPa N=2.4×10~5 cycles),demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC particles reinforced 6061 Al alloy composite.     

Worn surface characteristics of Cu-based powder metallurgy bake materials for aircraft

Cu-based powder metallurgy brake materials are used for aircraft widely and successfully.The characteristics of worn surface of Cu-based powder metallurgy brake materials for aircraft after working under service condition were studied,and two main wear mechanisms were discussed.The results show that the main components of worn surface are graphite,SiO2,Fe,Cu and oxide of Fe(Fe3O4 and FeO);the worn surface can be divided into three zones:severe wear zone,mild wear zone,and low wear zone; fatigue wear and grain wear are the main wear mechanisms of Cu-based materials.Some debris kept between brake discs reduce the wear rate to a certain extent by taking part in the regeneration of friction film.     

Optimum design of welding transformer

Welding transformer is widely used in industry manufacturing,depleting a large Portion of electricity energy.Based on modern computer and mathematical programming,Optimun design of electro-magnetic devicesleads to highly efficient use of energr and materials.Arc welding transformer is optimized here.A mathematical model,considering both productive cost and operating losses,which is called ar Economical-through-Life transformer,is estab-lished.Mixed function method,mixed dispersing variable method and improved orthogonal method have beenapplied to carry out the optimization calculations.Result shows that the power factor is quite important in an Econmi-cal-through-Life transformer,and that some principles must be followed in the design work.Also discussed are the ad-vantages and disadvantages of the three methods.In the end,the prospect of optimum design of welding transformer isforecast.     

Particles migration behavior during laser keyhole welding of ZLIO1/TiB2 composites

Particle redistribution occurred with the flow of pool fluid in laser welding aluminum composites. In order to investigate particle migration behavior, a numerical model was established on laser welding of ZL101-TiB2 composite. TiB2 migration coupling with fluid was realized. The volume-of-fluid (VOF) method was employed to track free fluid surfaces. The travel heat source was realized utilizing the workpiece motion in place of heat source motion, which made the heat load stable. Melting and evaporation enthalpy, recoil force, surface tension and buoyancy were considered in this model. Through the calculation it showed that the simulated weld cross section shape and particle distribution were in good agreement with experimental results.     

NICKEL-BASED ALLOYS IN GE AIRCRAFT TURBINES:PAST,PRESENT & FUTURE

Improvements in materials have been critical to advances in the propulsion system. Over the past 50 years, many improvements have been made to nickel-based superalloys to satisfy design requirements; several key developments will be highlighted. Today, millions of pounds of superalloys are annually produced for use in turbine blades, vanes, disks, cases, and frames throughout the engine. Looking to the future, several themes emerge, although predicting the future is inherently risky.     

Weldability and weld performance of candidate nickel base superalloys for advanced ultrasupercritical fossil power plants part I: fundamentals

Abstract

Fossil fuel will continue to be the major source of energy for the foreseeable future. To meet the demand for clean and affordable energy, an increase in the operating efficiency of fossil fired power plants is necessary. There are several initiatives worldwide to achieve efficiencies >45% higher heating value (HHV) through an increase in steam temperature (700 to 760°C) and pressure (27.6 to 34.5?MPa). Realising this goal requires materials with excellent creep rupture properties and corrosion resistance at elevated temperatures. In order to accomplish this, three classes of materials have been identified: creep strength enhanced ferritic steels, austenitic stainless steels and nickel base superalloys. Although new alloys have been designed and developed to meet this need, welding can have a significant and often detrimental effect on the required mechanical and corrosion resistant properties. Two previous papers addressed the welding and weldability of ferritic and austenitic stainless steels. Welding and weldability of nickel base alloys will be discussed in a two part paper. In this paper, the primary focus will be on the fundamentals of welding and weldability of Ni base superalloys.     

New method to diffusion bond superalloys

Abstract

A new method for diffusion bonding nickel base and cobalt base superalloys has been developed, which is based on non-chemical oxide removal before the bonding process. Using this method, diffusion bonds were produced in nickel base and cobalt base superalloys with 'virtually invisible' bond interfaces and compositions very close to the bulk alloys. The bonding time required is about 1 h and the results of severe mechanical tests of the bonded samples, including directionally solidified (DS), single crystal and dissimilar superalloys, are very promising. The new oxide removal method is very rapid, does not require the use of any sophisticated equipment and is not a costly process. The high temperature properties of bonded samples are currently being investigated. European and USA patents have been applied for and the details of this new method are to be published in the future.     

Novel design concepts for gamma-base titanium aluminide alloys

Two-phase titanium aluminide alloys are being considered as light-weight materials to replace nickel-base superalloys for some high temperature applications in energy conversion systems. Thus, their mechanical properties have to be assessed against the high standard set by the superalloys currently in use. In this respect most titanium aluminides are particularly inferior in high temperature strength and creep resistance even if these properties are related to density. In an attempt to overcome these problems several studies have been performed on titanium aluminides which have been subjected to solid solution and precipitation hardening. The intention of the present study is to examine more closely these strengthening processes in order to assess their potential for extending the service range of the titanium aluminides towards higher temperatures. There is growing evidence that two-phase titanium aluminides, microalloyed with carbon or niobium, can provide the necessary performance. Particular emphasis will be placed on processing routes acceptable for these materials.     

Pt-Al涂层进展

综述了Pt-Al涂层的发展历史,讨论了不同涂层的表 面形貌以及可能的形成机制.     

N元素对FGH96高温合金析出相的影响

基于Thermo-Calc热力学计算软件及相应的Ni基数据库,计算了含N与不含N时FGH96高温合金中可能的平衡析出相,并用Scheil-Gulliver凝固模型对两种合金进行了凝固模拟.对两种合金的计算结果进行比较,从热力学角度分析研究了N对FGH96高温合金中析出相的影响.结果表明,N元素主要影响一次碳化物的析出行为,而对其他相的析出影响很小;在含有少量N的FGH96合金中,在液相线温度以上可析出Ti、N为主要成分的M(C,N)相,而不含N时,只有当固相率达到70％时才会从残余液相中析出MC型碳化物.由计算得出的一次碳化物的成分变化结果,并结合扫描电镜图和能谱分析结果可推断出,FGH96高温合金中含有N时,首先从液态合金中析出以TiN为主要成分的M(C,N)相,随后的MC型碳化物会在其表面析出,形成以TiN为核心的一次碳化物.     

Precision Cast vs. Wrought Superalloys

The advancement of jet engine technology has traditionally given wrought superalloys eminence when design calls for both reasonable high temperature strength and dynamic fracture reliability. Despite the attractiveness of cast superalloys for their improved buy-to-fly ratios and higher strengthening γ volume fractions, the expansion of polycrystalline castings into the more critical of the superalloy applications has been prevented by a lack of sufficient micro structural control in casting technology. Recently, however, advances in casting technology are making possible the production of defect tolerant superalloy castings with improved fracture reliability. This new generation of superalloy castings now offers serious competition to wrought superalloys. Never before have wrought superalloys been so seriously threatened by their cast counterparts.     

Superalloys for Aerospace Application

The present and future uses of the superalloys in aerospace are outlined. The properties of super-alloys in the 1000° to 1900°F range are listed, including fabrication methods and oxidation protection. Compositions of various superalloys are tabulated, and oxidation-resistance coatings are illustrated.     

单晶镍基高温合金的非平衡凝固

单晶高温合金具有优异的高温力学性能。本文着重介绍单晶高温合金的非平衡凝固方面的部分有趣的研究结果:包括固液界面的形态选择,从而提示如何合适控制定向凝固工艺参数;在大温度梯度下和在侧向约束条件下的定向凝固,首次发现存在一个无(γ+γ′)共晶区和TiC的上浮现象;在加快冷却速度时,还发现从未报导过的TiC的奇异形态以及其它一些亚稳相。     

RESEARCH AND DEVELOPMENT OF HIGH TEMPERATURE STRUCTURAL MATERIALS FOR AERO-ENGINE APPLICATIONS

The status of research, development of superalloys and materials processing ＆ fabrication technologies for aero-engine applications in China Aviation Industry, with an emphasis on recent achievements at BIAM including directionally solidified and single crystal superalloys for blade and vane applications, wrought superqlloys for aero-engine disks and rings, and powder metalurgy （PM） superalloys for high performance disk applications were described. It was also reviewed the development of new class of high temperature structural materials, such as structural intermetallics, and advanced material processing technologies including rapid solidification, spray forming and so on. The trends of research and development of the above mentioned superalloys and processing technologies are outlined. Cast, wrought and PM superalloys are the workhorse materials for the hot section of current aero-engines. New high temperature materials and advanced processing technologies have been and will be the subject of study. It is speculated that high performance, high purity and low cost superalloys and technologies will play key roles in aero-engines.