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1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2007 SAE International All rights reserved. No part of this publication m
3、ay be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org AS1814C AEROSPACE STANDARD Issued 1983-07 Reaffirmed 2003-04 Revised 2007-12 Superseding AS1814B Terminology for Titanium Microstructures RATIONALE AS1814C results from a five year review and update of this specifica
5、tion. 1. SCOPE 1.1 This list of terms, with accompanying photomicrographs where appropriate, is intended as a guide for use in the preparation of material specifications. 1.2 The terms and photomicrographs are intended to present definitions only; they do not define either acceptance limits or minim
6、um standards of quality. 1.3 Listings are not grouped by specific alloys or conditions and represent the typical microstructures wherever they occur. 1.4 Etchants used for the microstructures shown are stated. Where “Krolls“ is stated, the composition is 10 ml HF, 30 ml HNO3, and 50 ml water (H2O).
7、1.5 Other common etchants are listed in ASTM E 407, Microetching Metals and Alloys. 2. TERMINOLOGY 2.1 Acicular Alpha A product of nucleation and growth or an athermal (martensitic) transformation from beta to the lower temperature allotropic alpha phase. It may be needle-like, lenticular, or flatte
8、ned bar morphology in three dimensions. Its typical aspect ratio is about 10:1. (Figure 1) 2.2 Aged Beta A beta matrix in which alpha, typically fine, has precipitated as a result of aging or cooling from a temperature high in the alpha-beta phase field. (Figure 2). 2.3 Alpha The low temperature all
9、otrope of titanium with a hexagonal, close-packed crystal structure. (Figure 3) Copyright SAE International Provided by IHS under license with SAELicensee=MHI - NAGOYA related to 3944000/3944000013 Not for Resale, 02/16/2008 01:38:07 MSTNo reproduction or networking permitted without license from IH
10、S -,-,- SAE AS1814C - 2 - 2.4 Alpha 2 Structure A structure consisting of an ordered alpha phase, such as Ti3 (Al, Sn) found in highly stabilized alpha. Defined by selected area diffraction, not optical metallography. 2.5 Alpha-Beta Structure A microstructure which contains both alpha and beta as th
11、e principal phases at a specific temperature. It is composed of alpha, transformed beta, and retained beta. Structure shown in Figure 4 is typical of mill annealed Ti 6Al-4V; similar structure shown in Figure 18 is more typical of recrystallization annealed Ti 6Al-4V. 2.6 Alpha Case The oxygen, enri
12、ched, alpha-stabilized surface which results from elevated temperature exposure to environments containing oxygen or air. (Figures 5A and 5B) Alpha case is normally hard, brittle, and considered detrimental. 2.7 Alpha Prime A supersaturated, acicular nonequilibrium hexagonal phase formed by a diffus
13、ionless transformation of the beta phase. It occurs when cooling rates are too high to permit transformation by nucleation and growth. It exhibits an aspect ratio of 10:1 or greater. Also known as martensite or martensite alpha. (Figure 6) 2.8 Alpha Double Prime (Orthorhombic Martensite) A supersatu
14、rated nonequilibrium orthorhombic phase formed by a diffusionless transformation of the beta phase in certain alloys. It occurs when cooling rates are too high to permit transformation by nucleation and growth. It may be strain induced during working operations and may be avoided by appropriate in-p
15、rocess annealing treatments. 2.9 Alpha Stabilizer An alloying element which dissolves preferentially in the alpha phase and raises the alpha-beta transformation temperature. Aluminum is the most commonly used alpha stabilizer. Interstitial elements such as oxygen and nitrogen are also potent alpha s
16、tabilizing elements. 2.10 Alpha Stringer Platelet alpha that has been elongated and distorted by metal working but not broken up or recrystallized. Also called “Wormy Alpha“ or “Stringy Alpha”. (Figure 19). 2.11 Alpha-Transus The temperature that alpha begins to revert to beta. 2.12 Basketweave Alph
17、a platelets, with or without interweaved beta platelets, that occur in colonies. Also known as Widmanstatten. Forms during cooling through the beta transus at intermediate cooling rates. (Figure 7A) 2.13 Beta The allotrope of titanium with a body-centered cubic crystal structure occurring at tempera
18、tures between the solidification of molten titanium and the beta transus, i.e., the high temperature allotrope. Copyright SAE International Provided by IHS under license with SAELicensee=MHI - NAGOYA related to 3944000/3944000013 Not for Resale, 02/16/2008 01:38:07 MSTNo reproduction or networking p
19、ermitted without license from IHS -,-,- SAE AS1814C - 3 - 2.14 Beta Eutectoid Stabilizer An alloying element that dissolves preferentially in the beta phase, lowers the alpha-beta to beta transformation temperature, under equilibrium conditions, and results in the beta decomposition to alpha plus a
20、compound. This is a eutectoid reaction. Commonly used beta eutectoid forming elements are iron, nickel, chromium, and manganese. 2.15 Beta Fleck Beta flecks have reduced amounts of, or no, primary alpha which may exhibit a morphology different from the primary alpha in the surrounding alpha-beta mat
21、rix and/or absence of alpha stabilizers such as oxygen or aluminum. The flecks are then seen by the reduced or lack of alpha within the beta fleck. (Figure 8) 2.16 Beta Isomorphous Stabilizer An alloying element that is soluble in beta titanium in all proportions. It lowers the alpha-beta to beta tr
22、ansformation temperature without a eutectoid reaction and forms a continuous series of solid solutions with beta titanium. Commonly used beta isomorphous forming elements are vanadium, molybdenum, and zirconium. 2.17 Beta Transus The temperature that designates the phase boundary between the alpha p
23、lus beta and beta fields. Commercially pure grades transform in a range of 1630 to 1760 F (890 to 960 C) depending upon oxygen and iron content. In general, aircraft alloys vary in transformation temperature from 1380 to 1900 F (750 to 1040 C). 2.18 Blocky Alpha Alpha phase which is considerably lar
24、ger and more polygonal in appearance than the primary alpha present. It may be induced by metal working and has an aspect ratio of 3:1 or higher although its aspect ratio may be near 1:1 (less common). It may result from extended exposure high in the alpha-beta phase field following rapid or slow co
25、oling through the beta transus during forging or heat treating operations. It may be removed by beta recrystallization or by all-beta working followed by further alpha-beta work. May accompany grain boundary alpha or even have its origin as large grain boundary alpha or coarse alpha platelets. Micro
26、hardness not significantly different from surrounding normal alpha-beta matrix. (Figure 9) 2.19 Colonies Regions within prior beta grains with alpha platelets having nearly identical orientations. In commercially pure titanium, colonies often have serrated boundaries. Colonies arise as transformatio
27、n products during cooling from the beta field at cooling rates slow enough to allow platelet nucleation and growth. (Figures 7A and 7B) 2.20 Elongated Alpha The hexagonal crystal phase appearing as stringer-like arrays, considerably larger in appearance than the primary alpha. Commonly exhibits an a
28、spect ratio of 3:1 or higher. (Figures 10 and 11) 2.21 Equiaxed Structure A polygonal or spheroidal microstructural feature having approximately equal dimensions in all directions. In alpha-beta titanium alloys, such a term commonly refers to a microstructure in which most of the alpha phase appears
29、 spheroidal, primarily in the transverse direction. (Figures 3, 4, and Figure 18) 2.22 Frequency of Occurrence A referee determination by viewing 50 fields, 4 in x 5 in (102 mm x 127 mm), projected at 100X. The number of fields containing the feature of interest is divided by the total number of fie
30、lds viewed to represent the lot, thus arriving at a percentage. Copyright SAE International Provided by IHS under license with SAELicensee=MHI - NAGOYA related to 3944000/3944000013 Not for Resale, 02/16/2008 01:38:07 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE AS18
31、14C - 4 - 2.23 Gamma Structure An ordered structure of titanium-aluminum compound with a stoichiometric ratio TiAl and face-centered tetragonal crystal structure. 2.24 Globular Alpha A spheroidal form of equiaxed alpha. (Figure 4) 2.25 Grain Boundary Alpha Alpha outlining prior beta grain boundaries
32、. It may be continuous unless broken up by subsequent work. Also may accompany blocky alpha. Occurs by slow cooling from the beta field into alpha-beta field. (Figures 1, 7B, 9, 11, and 12) 2.26 High Aluminum Defect (HAD) An aluminum-rich alpha stabilized region containing an abnormally large amount
33、 of aluminum which may extend across a large number of beta grains. It contains an inordinate fraction of primary alpha but has a microhardness only slightly higher than the adjacent matrix. These are also known as Type II defects. (Figures 13 and 14) 2.27 High Density Inclusion (HDI) A region with
34、a concentration of elements, usually tungsten, molybdenum, tungsten carbide, or residuals of high melting point master alloys containing molybdenum, having a higher density than the matrix. Regions are readily detectable by X- ray and will appear brighter than the matrix. 2.28 High Interstitial Defe
35、ct (HID) Interstitially stabilized alpha phase region of substantially higher hardness and lower ductility than surrounding material. It arises from melting titanium in the presence of nitrogen, oxygen, or carbon. HID typicaly have a diffusion zone. They are commonly called Type I defects or low-den
36、sity inclusions (LDI). HIDs often associated with voids and cracks. (Figures 15 and 16) 2.29 Hydride Phase The phase TiHx formed in titanium when the hydrogen content exceeds the solubility limit. Hydrogen and, therefore, hydrides tend to accumulate at areas of high residual tensile stresses. (Figur
37、es 17A and 17B) 2.30 Interstitial Element An element with relatively small atomic diameter that can assume position in the interstices of the titanium crystal lattice. Common examples are oxygen, nitrogen, hydrogen, and carbon. 2.31 Intergranular Beta Beta phase situated between alpha grains. It may
38、 be at grain corners as in the case of equiaxed alpha type of microstructures in alloys having low beta stabilizer content. Because it is the original phase from which alpha is formed, it is usually the continuous phase in two phase microstructures. (Figure 18) 2.32 Intermetallic Compound A phase in
39、 an alloy system which usually occurs at a definite atomic ratio and exhibits a narrow solubility range, such as Ti2Fe, Ti-Ni, or alpha 2. Nearly all such phases are brittle. Copyright SAE International Provided by IHS under license with SAELicensee=MHI - NAGOYA related to 3944000/3944000013 Not for
40、 Resale, 02/16/2008 01:38:07 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE AS1814C - 5 - 2.33 Martensite See “Alpha Prime“, “Alpha Double Prime” (orthorhombic martensite in some significantly beta stabilized alloys). 2.34 Matrix The constituent which forms the continu
41、ous phase of a two or more phase microstructure. 2.35 Metastable Beta A nonequilibrium phase composition that can be partially transformed to martensite, alpha, or eutectoid decomposition products with thermal or strain energy activation during subsequent processing or service exposure. 2.36 Mf The
42、temperature at which the martensite reaction is complete. 2.37 Ms The maximum temperature at which a martensite reaction begins upon cooling from the beta phase or high in the alpha- beta field. 2.38 Omega A nonequilibrium, submicroscopic phase which can be formed either athermally or isothermally p
43、receding the formation of alpha from beta. It occurs in metastable beta alloys, alpha-plus-beta alloys rich in beta content, and CP titanium, and leads to severe embrittlement in metastable beta alloys or alpha-beta alloys rich in beta content. Athermal omega is believed to form without change in co
44、mposition and is analagous to martensite. Isothermal omega is generally formed by aging a retained beta structure in the 392 to 932 F (200 to 500 C) temperature range. 2.39 Ordered Structure The orderly or periodic arrangement of solute atoms on the lattice sites of the solvent. 2.40 Platelet Alpha
45、A relatively coarse acicular alpha, usually with low aspect ratios. This microstructure arises from cooling alpha or alpha- beta alloys at a slow rate from temperatures that a significant fraction of beta phase exists. (Figure 10) 2.41 Primary Alpha The allotrope of titanium with a hexagonal, close-
46、packed crystal structure which is retained from the last high temperature alpha-beta heating. (Figure 4) 2.42 Prior Beta Grain Size Size of beta grains established during the most recent beta field excursion. The grains may be distorted by subsequent subtransus deformation. The beta grain boundaries
47、 may be obscured by a superimposed alpha-beta microstructure and detectable only by special techniques. (Figure 12) 2.43 Stringy Alpha See “Alpha Stringer”. (Figure 19) Copyright SAE International Provided by IHS under license with SAELicensee=MHI - NAGOYA related to 3944000/3944000013 Not for Resal
48、e, 02/16/2008 01:38:07 MSTNo reproduction or networking permitted without license from IHS -,-,- SAE AS1814C - 6 - 2.44 Substitutional Element An alloying element with an atom size and other features similar to the titanium atom, which can replace or substitute for the titanium atoms in the lattice and form a significant region of solid solution in the phase diagram. Such elements used in alloying titanium include but are not limited to aluminum, vanadium, molybdenum, chromium, iron, tin, and zirconium. 2.45 Transformed