JP2021134399A - PRODUCTION METHOD OF TiAl-BASED ALLOY, AND TiAl-BASED ALLOY - Google Patents
PRODUCTION METHOD OF TiAl-BASED ALLOY, AND TiAl-BASED ALLOY Download PDFInfo
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Abstract
Description
本開示は、ＴｉＡｌ基合金の製造方法およびＴｉＡｌ基合金に関するものである。 The present disclosure relates to a method for producing a TiAl-based alloy and a TiAl-based alloy.
精密部材の大量生産に適した製造方法として金属粉末射出成形（ＭＩＭ）法が知られている。 The metal powder injection molding (MIM) method is known as a manufacturing method suitable for mass production of precision members.
ＭＩＭ法は、バインダと金属粉末の混錬物を成形型内に射出して成形する方法である。ＭＩＭ法は、射出成形する工程と、バッチ処理で焼結する工程とを含む。 The MIM method is a method of injecting a kneaded product of a binder and a metal powder into a molding mold to mold it. The MIM method includes a step of injection molding and a step of sintering by batch processing.
特許文献１には、ＭＩＭ法によりタービンホイールの最終製品と近似した形状を有する焼結体を製造する技術が開示されている。
ＴｉＡｌ基合金は、他の耐熱合金に比べて鋳造性および鍛造性に劣る。その点において、ＭＩＭ法は、ＴｉＡｌ基合金の製造方法として有望である。 TiAl-based alloys are inferior in castability and forgeability to other heat-resistant alloys. In that respect, the MIM method is promising as a method for producing a TiAl-based alloy.
一方、ＭＩＭ法は焼結工程を含むため、ボイドの除去が課題となる。 On the other hand, since the MIM method includes a sintering step, removal of voids becomes an issue.
他の耐熱合金に比べて、ＴｉＡｌ基合金の焼結温度は融点に近い。融点に近い温度で焼結する場合、ＴｉＡｌ基合金が変形することが懸念される。焼結炉の中に複数の成形体を並べて焼結させると、炉内に温度分布に偏りが生じることがある。炉内温度が均一にならないと、局所的に融点近くまで温度が上がり、変形が生じる可能性が高くなる。 Compared to other heat-resistant alloys, the sintering temperature of TiAl-based alloys is closer to the melting point. When sintering at a temperature close to the melting point, there is a concern that the TiAl-based alloy may be deformed. When a plurality of molded bodies are arranged side by side in a sintering furnace and sintered, the temperature distribution may be biased in the furnace. If the temperature inside the furnace is not uniform, the temperature will rise locally to near the melting point, increasing the possibility of deformation.
焼結温度を下げると、変形は回避できるが、ボイドが残存しやすく（＝焼結密度が低く）なる。焼結密度の低いＴｉＡｌ基合金では、割れが発生しやすい。 When the sintering temperature is lowered, deformation can be avoided, but voids are likely to remain (= sintering density is low). TiAl-based alloys with a low sintering density are prone to cracking.
特許文献１では、焼結時に生じた変形をプレス加工により矯正している。
In
このような事情から、ＴｉＡｌ基合金では、焼結密度の高い高品質な焼結体を得ることが難しく、焼結工程における歩留まりが低いことが問題であった。 Under these circumstances, it is difficult to obtain a high-quality sintered body having a high sintering density with a TiAl-based alloy, and there is a problem that the yield in the sintering process is low.
本開示は、このような事情に鑑みてなされたものであって、より安定的に焼結性を高められるＴｉＡｌ基合金の製造方法およびＴｉＡｌ基合金を提供することを目的とする。 The present disclosure has been made in view of such circumstances, and an object of the present invention is to provide a method for producing a TiAl-based alloy and a TiAl-based alloy capable of more stably improving sinterability.
上記課題を解決するために、本開示のＴｉＡｌ基合金の製造方法およびＴｉＡｌ基合金は以下の手段を採用する。 In order to solve the above problems, the method for producing a TiAl-based alloy and the TiAl-based alloy of the present disclosure employ the following means.
本開示は、金属粉末射出成形法を用いたＴｉＡｌ基合金の製造方法であって、ＴｉＡｌ基合金の状態図からβ＋α／α変態温度を確認し、前記β＋α／α変態温度以上のβ相存在温度域の温度で焼結するＴｉＡｌ基合金の製造方法を提供する。 The present disclosure is a method for producing a TiAl-based alloy using a metal powder injection molding method. The β + α / α transformation temperature is confirmed from the phase diagram of the TiAl-based alloy, and the β-phase existence temperature equal to or higher than the β + α / α transformation temperature is present. Provided is a method for producing a TiAl-based alloy that is sintered at a temperature in the range.
また本開示は、上記製造方法で製造されたＴｉＡｌ基合金を提供する。 The present disclosure also provides a TiAl-based alloy produced by the above production method.
本開示によれば、β相の体積率が高くなる温度域で焼結を実施することで、安定的に焼結性を高め、高品質の焼結体を得られる。 According to the present disclosure, by performing sintering in a temperature range in which the volume fraction of the β phase is high, the sinterability is stably improved, and a high-quality sintered body can be obtained.
本実施形態に係るＴｉＡｌ基合金の製造方法は、ガスタービンエンジンの低圧タービン動翼、ガスタービンエンジンの高圧コンプレッサー動翼、およびターボチャージャーのタービンホイール等へ適用されうる。 The method for producing a TiAl-based alloy according to the present embodiment can be applied to a low-pressure turbine moving blade of a gas turbine engine, a high-pressure compressor moving blade of a gas turbine engine, a turbine wheel of a turbocharger, or the like.
本実施形態では、金属粉末射出成形（ＭＩＭ）法を用いてＴｉＡｌ基合金を製造する。図１に、ＭＩＭ法の手順を示す。ＭＩＭ法は、（Ｓ１）混錬および造粒、（Ｓ２）射出成形、（Ｓ３）脱脂、（Ｓ４）焼結の工程を含む。本実施形態に係るＴｉＡｌ基合金の製造方法は、上記（Ｓ４）焼結の後に、（Ｓ５）焼結体を熱処理する工程を含んでもよい。 In this embodiment, a TiAl-based alloy is produced using a metal powder injection molding (MIM) method. FIG. 1 shows the procedure of the MIM method. The MIM method includes (S1) kneading and granulation, (S2) injection molding, (S3) degreasing, and (S4) sintering. The method for producing a TiAl-based alloy according to the present embodiment may include a step of heat-treating the (S5) sintered body after the above (S4) sintering.
ＴｉＡｌ基合金の製造には、原料として金属粉末およびバインダが用いられる。 Metal powders and binders are used as raw materials in the production of TiAl-based alloys.
金属粉末は、Ｔｉ粉末およびＡｌ粉末を含む。金属粉末は、第３元素、または第３元素および第４元素としてβ安定化元素の粉末を含んでもよい。β安定化元素としては、Ｖ，Ｎｂ，Ｃｒ，ＭｏおよびＭｎが挙げられる。 The metal powder includes Ti powder and Al powder. The metal powder may contain powders of β-stabilizing elements as the third element, or the third and fourth elements. Examples of β-stabilizing elements include V, Nb, Cr, Mo and Mn.
金属粉末は、ガスアトマイズ法、水アトマイズ法、および回転電極法等で製造された粉であってよい。金属粉末は、ガスアトマイズ法で製造された粉であることが好ましい。 The metal powder may be a powder produced by a gas atomizing method, a water atomizing method, a rotating electrode method, or the like. The metal powder is preferably a powder produced by the gas atomization method.
金属粉末の粒径は、４５μｍ以下、好ましくは３０μｍ以下であるとよい。上限値を超えると、射出成形時における成形素材の流動性が低くなり、充填不良が発生しやすくなる。また、粉末間の空隙が大きくなり焼結体の密度が低下する。 The particle size of the metal powder is preferably 45 μm or less, preferably 30 μm or less. If the upper limit is exceeded, the fluidity of the molding material during injection molding becomes low, and filling defects are likely to occur. In addition, the voids between the powders become large and the density of the sintered body decreases.
例えば、金属粉末は、ガスアトマイズ法で作製した粉を分級により平均粒径４５μｍ以下に調整された粉を用いることができる。 For example, as the metal powder, a powder prepared by the gas atomizing method and adjusted to an average particle size of 45 μm or less by classification can be used.
バインダは、原料の粉末同士をつなぎ合わせるものである。バインダは、（Ｓ２）射出成形の際に、金型の内部に射出成形材料が完全に充填されるように、射出成形材料に流動性（粘度）を付与できる材料であればよい。バインダは、ポリアセタール、ポリプロピレン、ポリエチレン、エチレン酢酸ビニル、またはアクリル樹脂などの有機材料からなる粉末である。 A binder is a binder that joins raw material powders together. The binder may be any material that can impart fluidity (viscosity) to the injection molding material so that the injection molding material is completely filled inside the mold during (S2) injection molding. The binder is a powder made of an organic material such as polyacetal, polypropylene, polyethylene, ethylene vinyl acetate, or an acrylic resin.
原料には、さらに、ワックスまたは他の潤滑剤等が含まれていてもよい。 The raw material may further contain wax or other lubricants and the like.
（Ｓ１）混錬および造粒
原料（金属粉末とバインダとを含む）を混錬機に投入し、加圧および加熱しながら混錬する。粘土状の混錬物を造粒機にかけ、ペレット（射出成形材料）を得る。
(S1) Kneading and Granulation Raw materials (including metal powder and binder) are put into a kneader and kneaded while being pressurized and heated. The clay-like kneaded product is subjected to a granulation machine to obtain pellets (injection molding material).
バインダの添加量は、混錬物全体のおおよそ３０ｗｔ％以上４５ｗｔ％以下であることが好ましい。バインダの添加量は、射出成形性および焼結性を考慮し、合金成分、製品形状、および量産仕様に合わせて調整する。その際、合金原料、バインダの種類および製造条件により最終製品に含まれる酸素量は変化する。本実施形態では、概ね１０００ｐｐｍ以上の高酸素合金製品が成形される。 The amount of the binder added is preferably approximately 30 wt% or more and 45 wt% or less of the entire kneaded product. The amount of binder added is adjusted according to the alloy composition, product shape, and mass production specifications in consideration of injection moldability and sinterability. At that time, the amount of oxygen contained in the final product changes depending on the alloy raw material, the type of binder, and the manufacturing conditions. In this embodiment, a high oxygen alloy product of about 1000 ppm or more is molded.
（Ｓ２）射出成形
射出成形材料を射出成形機に入れ、可塑化して金型のキャビティ内に射出成形する。これにより所望形状の成形体（グリーン体）が得られる。
(S2) Injection Molding The injection molding material is put into an injection molding machine, plasticized, and injection molded into the cavity of the mold. As a result, a molded product (green body) having a desired shape can be obtained.
（Ｓ３）脱脂
グリーン体を炉に入れ、減圧下およびガス雰囲気で加熱しバインダを揮散させる（加熱脱脂）。炉は、バッチ式または連続式のいずれであってもよい。これにより、バインダが除去されたブラウン体が得られる。ここでガスを使用する場合は、アルゴン、窒素あるいは硝酸ガス等であってよい。
(S3) Solvent degreasing The green body is placed in a furnace and heated under reduced pressure and in a gas atmosphere to volatilize the binder (heat degreasing). The furnace may be either batch or continuous. As a result, a brown body from which the binder has been removed is obtained. When a gas is used here, it may be argon, nitrogen, nitric acid gas or the like.
加熱脱脂は、金属粉末同士が結合されない程度の温度で実施される。バインダ成分および圧力にもよるが、概ね３３３Ｋ以上８７３Ｋ以下（６０℃以上６００℃以下）のバインダが揮散する温度で実施されうる。該加熱は、焼結よりも低い温度で実施される。 The heat degreasing is carried out at a temperature at which the metal powders are not bonded to each other. Although it depends on the binder component and the pressure, it can be carried out at a temperature at which the binder of about 333K or more and 873K or less (60 ° C. or more and 600 ° C. or less) volatilizes. The heating is carried out at a temperature lower than that of sintering.
なお、脱脂は溶媒を用いた公知の脱脂法により実施されてもよく、加熱脱脂と組み合わせても良い。その場合、グリーン体を溶媒に浸漬し、バインダを抽出する（溶媒脱脂）。抽出するバインダ成分によるが、溶媒には有機溶剤または水が使用されうる。実施温度は、室温から溶媒の沸点以下であり得る。 The degreasing may be carried out by a known degreasing method using a solvent, or may be combined with heat degreasing. In that case, the green body is immersed in a solvent to extract the binder (solvent degreasing). Depending on the binder component to be extracted, an organic solvent or water can be used as the solvent. The implementation temperature can be from room temperature to below the boiling point of the solvent.
（Ｓ４）焼結
ブラウン体を焼結炉に入れ、β＋α／α変態温度（Ｔβ）以上の温度で焼結する。β＋α／α変態温度は、予め、ＴｉＡｌ基合金の状態図から確認しておく。所望の合金成分で状態図が不明である場合は、類似合金の状態図からβ＋α／α変態温度を推定する。焼結時間は、適宜、焼結試験等により高い相対密度、例えば相対密度９５％以上が得られる時間等を設定する。
(S4) Sintering The brown body is placed in a sintering furnace and sintered at a temperature equal to or higher than the β + α / α transformation temperature (T β). The β + α / α transformation temperature is confirmed in advance from the phase diagram of the TiAl-based alloy. If the phase diagram of the desired alloy component is unknown, the β + α / α transformation temperature is estimated from the phase diagram of similar alloys. The sintering time is appropriately set to a time at which a high relative density, for example, a relative density of 95% or more can be obtained by a sintering test or the like.
β相存在温度域は、β＋α相温度域、β単相温度域を含む。焼結は、焼結合金の用途に従い、β＋α相温度域あるいはβ単相温度域で実施する。 The β-phase existing temperature range includes the β + α-phase temperature range and the β single-phase temperature range. Sintering is carried out in the β + α phase temperature range or the β single phase temperature range, depending on the application of the sintered alloy.
なお、β相存在温度域で焼結（本焼結）する前に、仮焼結させてもよい。仮焼結では、金属粒子同士が緩やかに結合（ネッキング）される。仮焼結は、脱脂の加熱よりも高い温度であり、かつ、β変態開始温度よりも低い温度で実施される。例えば、仮焼結温度は、１３２３Ｋ以上１５２３Ｋ以下（１０５０℃以上１２５０℃以下）で実施されうる。合金成分にもよるが、概ね仮焼結温度が１３２３Ｋ未満であるとネッキングが不十分となり形状が保持できない。焼結温度が１５２３Ｋより高いと部分的に焼結が進行し予定外の収縮変形が発生してしまうことが懸念される。仮焼結は、３０分以上２時間以下の保持時間で実施され得る。 It should be noted that tentative sintering may be performed before sintering (main sintering) in the β phase existing temperature range. In the tentative sintering, the metal particles are loosely bonded (necked) to each other. Temporary sintering is carried out at a temperature higher than the heating of degreasing and lower than the β transformation start temperature. For example, the tentative sintering temperature can be carried out at 1323 K or more and 1523 K or less (1050 ° C or more and 1250 ° C or less). Although it depends on the alloy component, if the temporary sintering temperature is less than 1323 K, the necking becomes insufficient and the shape cannot be maintained. If the sintering temperature is higher than 1523K, there is a concern that sintering will partially proceed and unplanned shrinkage deformation will occur. Temporary sintering can be carried out with a holding time of 30 minutes or more and 2 hours or less.
（Ｓ５）熱処理
（Ｓ４）の後、必要に応じて、焼結体を熱間静水圧プレス（ＨＩＰ）法により熱処理する。ＨＩＰ処理は、焼結温度よりも５０℃以上２００℃以下程度低い温度で１００ＭＰａ以上１８０ＭＰａ以下程度の高圧で実施するとよい。これにより、ボイド等の内部欠陥が消滅し、より健全な焼結体が得られる。
(S5) Heat treatment After (S4), if necessary, the sintered body is heat-treated by a hot hydrostatic press (HIP) method. The HIP treatment may be carried out at a temperature 50 ° C. or higher and 200 ° C. or lower lower than the sintering temperature and at a high pressure of 100 MPa or higher and 180 MPa or lower. As a result, internal defects such as voids disappear, and a healthier sintered body can be obtained.
ＨＩＰ処理後、焼結体をＨＩＰ処理温度またはそれ以下の温度で所定時間保持してもよい。 After the HIP treatment, the sintered body may be held at the HIP treatment temperature or lower for a predetermined time.
以下に、本実施形態に係るＴｉＡｌ基合金の製造方法の作用効果について説明する。 The effects of the method for producing a TiAl-based alloy according to the present embodiment will be described below.
（状態図）
図２〜４に、ＴｉＡｌ基合金の状態図を例示する。図２は、Ｔｉ−Ａｌ−Ｎｂ−Ｃｒ四元系（４４ａｔ．％Ａｌ）の状態図である。同図において、横軸はＮｂおよびＣｒの含有量（ａｔ．％）、縦軸は温度（Ｋ）である。図３は、Ｔｉ−Ａｌ−Ｃｒ三元系（４４ａｔ．％Ａｌ）の状態図である。同図において、横軸はＣｒの含有量（ａｔ．％）、縦軸は温度（Ｋ）である。図４は、Ｔｉ−Ａｌ−Ｎｂ三元系（４７ａｔ．％Ａｌ）の状態図である。同図において、横軸はＮｂの含有量（ａｔ．％）、縦軸は温度（Ｋ）である。
(State diagram)
2 to 4 show a phase diagram of the TiAl-based alloy. FIG. 2 is a phase diagram of the Ti-Al-Nb-Cr quaternary system (44 at.% Al). In the figure, the horizontal axis represents the Nb and Cr contents (at.%), And the vertical axis represents the temperature (K). FIG. 3 is a phase diagram of the Ti—Al—Cr ternary system (44 at.% Al). In the figure, the horizontal axis represents the Cr content (at.%) And the vertical axis represents the temperature (K). FIG. 4 is a phase diagram of the Ti—Al—Nb ternary system (47 at.% Al). In the figure, the horizontal axis represents the Nb content (at.%) And the vertical axis represents the temperature (K).
いずれの状態図においても最も高い温度域にβ単相域があり、その下に（β＋α）２相域があり、さらにその下にα単相域が存在する。β＋α／α変態温度はα単相域と（β＋α）２相域の境界であり、これらの状態図から合金成分によってその境界の温度を把握することが可能である。 In any of the state diagrams, the β single-phase region is in the highest temperature region, the (β + α) two-phase region is below it, and the α single-phase region is further below. The β + α / α transformation temperature is the boundary between the α single-phase region and the (β + α) two-phase region, and it is possible to grasp the temperature of the boundary from the alloy components from these phase diagrams.
図２〜４において、β＋α，βとして示された領域がβ相存在温度領域となる。上記実施形態では、この温度域内の温度で焼結を実施する。より高温で焼結することで、β相の体積率を高くできる。 In FIGS. 2 to 4, the regions shown as β + α and β are the β phase existing temperature regions. In the above embodiment, sintering is performed at a temperature within this temperature range. By sintering at a higher temperature, the volume fraction of the β phase can be increased.
ＮｂおよびＣｒは、β安定化元素であるが、それらの相安定化能は異なる。そのため、図２〜４では、含まれるβ安定化元素の相安定化能に応じて、β＋α／α変態温度領も異なる。 Nb and Cr are β-stabilizing elements, but their phase-stabilizing abilities are different. Therefore, in FIGS. 2 to 4, the β + α / α transformation temperature range also differs depending on the phase stabilizing ability of the contained β-stabilizing element.
図２において、ＮｂおよびＣｒの含有量が６ａｔ．％を通る縦軸方向に延びる破線上に示すプロットは一般的な熱処理温度の例示である。〇が高温熱処理、●が中温熱処理、■が低温熱処理を示す。熱処理をβ相存在温度域にある温度で実施することでより焼結密度を効率的に高めることができる。 In FIG. 2, the contents of Nb and Cr are 6 at. The plot shown on the broken line extending in the vertical direction through% is an example of a general heat treatment temperature. 〇 indicates high temperature heat treatment, ● indicates medium temperature heat treatment, and ■ indicates low temperature heat treatment. By carrying out the heat treatment at a temperature within the β-phase existence temperature range, the sintering density can be increased more efficiently.
なお、図２〜４は、酸素含有量を考慮していない状態図をベースとしている。本発明者らの鋭意検討の結果、酸素含有量が増えると、変態温度がシフトするという知見が得られている。図２では、酸素含有量１．０ａｔ．％であることを考慮した場合の、α単相領域の上側の線を一点鎖線で例示する。 Note that FIGS. 2 to 4 are based on a phase diagram in which the oxygen content is not taken into consideration. As a result of diligent studies by the present inventors, it has been found that the transformation temperature shifts as the oxygen content increases. In FIG. 2, the oxygen content is 1.0 at. The upper line of the α single-phase region when considering that it is% is illustrated by the alternate long and short dash line.
酸素含有量１．０ａｔ．％を考慮した場合、酸素含有量を考慮しなかった場合と比較して、α単相領域の上側の線が図の右上方向に＋４０Ｋ程度シフトする。この結果から、ＮｂおよびＣｒの含有量と温度条件が同じであっても、酸素含有量の有無でβ＋α／α変態温度が変化することがわかる。そのため、β＋α／α変態温度を確認する際、酸素含有量を考慮することが望ましい。それによって、より確実に焼結時にβ相の体積率を増やすことができる。酸素含有量は、軟Ｘ線分光器を用いた軟Ｘ線分光法で測定できる。 Oxygen content 1.0 at. When% is taken into consideration, the upper line of the α single-phase region is shifted to the upper right of the figure by about + 40 K as compared with the case where the oxygen content is not taken into consideration. From this result, it can be seen that the β + α / α transformation temperature changes depending on the presence or absence of the oxygen content even if the Nb and Cr contents and the temperature conditions are the same. Therefore, it is desirable to consider the oxygen content when confirming the β + α / α transformation temperature. Thereby, the volume fraction of the β phase can be increased more reliably at the time of sintering. The oxygen content can be measured by soft X-ray spectroscopy using a soft X-ray spectrometer.
（β相体積率と相対密度との関係）
図５に、Ｔｉ−４４Ａｌ−４Ｃｒにおけるβ相の体積率と相対密度との関係を示す。図５は、Ｔｉ−Ａｌ−Ｃｒ三元系の状態図と焼結試験の結果に基づき作成した。同図において、縦軸は相対密度（％）、横軸はβ相体積率（％）である。
(Relationship between β-phase volume fraction and relative density)
FIG. 5 shows the relationship between the volume fraction of the β phase and the relative density in Ti-44Al-4Cr. FIG. 5 was created based on the phase diagram of the Ti—Al—Cr ternary system and the results of the sintering test. In the figure, the vertical axis represents the relative density (%) and the horizontal axis represents the β-phase volume fraction (%).
図５によれば、β相の体積率が高いほど、相対密度も高くなることが確認された。β相の体積率が５６％以上であれば、相対密度９５％以上を達成できる。焼結温度が高いほど、ＴｉＡｌ基合金の相対密度も高くなる。β相の体積率および状態図によれば、図５で相対密度９５％を達成できる焼結温度は、１６３１Ｋ（１３５８℃）以上となる。図５によれば、β相体積率が６８％（焼結温度１６５３Ｋ）で、９８％程度の高い相対密度が得られることが確認できる。 According to FIG. 5, it was confirmed that the higher the volume fraction of the β phase, the higher the relative density. If the volume fraction of the β phase is 56% or more, a relative density of 95% or more can be achieved. The higher the sintering temperature, the higher the relative density of the TiAl-based alloy. According to the volume fraction and phase diagram of the β phase, the sintering temperature at which the relative density of 95% can be achieved in FIG. 5 is 1631 K (1358 ° C.) or higher. According to FIG. 5, it can be confirmed that a high relative density of about 98% can be obtained when the β-phase volume fraction is 68% (sintering temperature 1653K).
図６に、Ｔｉ−４７Ａｌ−５Ｎｂにおけるβ相の体積率と相対密度との関係を示す。図６は、Ｔｉ−Ａｌ−Ｎｂ三元系の状態図と焼結試験の結果に基づき作成した。同図において、縦軸は相対密度（％）、横軸はβ相体積率（％）である。 FIG. 6 shows the relationship between the volume fraction of the β phase and the relative density in Ti-47Al-5Nb. FIG. 6 was created based on the phase diagram of the Ti-Al-Nb ternary system and the results of the sintering test. In the figure, the vertical axis represents the relative density (%) and the horizontal axis represents the β-phase volume fraction (%).
図６によれば、図５と同様に、β相の体積率が高いほど、相対密度も高くなることが確認された。β相の体積率が９４％以上であれば、相対密度９５％以上を達成できる。β相の体積率および状態図によれば、図６で相対密度９５％を達成できる焼結温度は、１７５６Ｋ（１４８３℃）となる。 According to FIG. 6, it was confirmed that the higher the volume fraction of the β phase, the higher the relative density, as in FIG. If the volume fraction of the β phase is 94% or more, a relative density of 95% or more can be achieved. According to the volume fraction and phase diagram of the β phase, the sintering temperature at which the relative density of 95% can be achieved in FIG. 6 is 1756 K (1483 ° C.).
（温度と相対密度との関係）
図７に、相対密度と温度との関係を示す。同図において、縦軸が相対密度（％）、横軸（下）は温度の逆数（１／Ｔ）（１０−４Ｋ−１）、横軸（上）は温度（Ｋ）、■がＴｉ−４４Ａｌ−４Ｃｒ、◆がＴｉ−４７Ａｌ−５Ｎｂである。
(Relationship between temperature and relative density)
FIG. 7 shows the relationship between the relative density and the temperature. In the figure, the vertical axis is the relative density (%), the horizontal axis (bottom) is the reciprocal of temperature (1 / T) (10 -4 K -1 ), the horizontal axis (top) is the temperature (K), and ■ is Ti. -44Al-4Cr, ◆ is Ti-47Al-5Nb.
図７によれば、Ｔｉ−４４Ａｌ−４ＣｒおよびＴｉ−４７Ａｌ−５Ｎｂのいずれにおいても、温度が高くなるほど、相対密度も高くなる。 According to FIG. 7, in both Ti-44Al-4Cr and Ti-47Al-5Nb, the higher the temperature, the higher the relative density.
図７によれば、Ｔｉ−４４Ａｌ−４Ｃｒは、Ｔｉ−４７Ａｌ−５Ｎｂよりも低い焼結温度であっても、Ｔｉ−４７Ａｌ−５Ｎｂと同等の相対密度となりうる。すなわち、同じ温度で焼結を実施する場合、Ｔｉ−４７Ａｌ−５ＮｂよりもＴｉ−４４Ａｌ−４Ｃｒの方がより短い時間で、相対密度を高くできる。 According to FIG. 7, Ti-44Al-4Cr can have a relative density equivalent to that of Ti-47Al-5Nb even at a sintering temperature lower than that of Ti-47Al-5Nb. That is, when sintering is performed at the same temperature, the relative density of Ti-44Al-4Cr can be increased in a shorter time than that of Ti-47Al-5Nb.
図７の一点鎖線は、Ｔｉ−４７Ａｌ−５Ｎｂのβ＋α／α変態温度である。Ｔｉ−４７Ａｌ−５Ｎｂにおけるβ＋α／α変態温度は、１７０３Ｋ付近である（図４参照）。β＋α／α変態温度より低い温度で焼結する場合、Ｔｉ−４７Ａｌ−５Ｎｂ中にβ相は存在しない。そのため、図７の一点鎖線よりも低温側では、Ｔｉ−４７Ａｌ−５Ｎｂの相対密度が低くなる。一方、β＋α／α変態温度を超えると、Ｔｉ−４７Ａｌ−５Ｎｂの相対密度は急激に上がる。この理由は、β相の体積率の増加である。 The alternate long and short dash line in FIG. 7 is the β + α / α transformation temperature of Ti-47Al-5Nb. The β + α / α transformation temperature at Ti-47Al-5Nb is around 1703K (see FIG. 4). When sintering at a temperature lower than the β + α / α transformation temperature, the β phase does not exist in Ti-47Al-5Nb. Therefore, the relative density of Ti-47Al-5Nb is lower on the lower temperature side than the alternate long and short dash line in FIG. On the other hand, when the β + α / α transformation temperature is exceeded, the relative density of Ti-47Al-5Nb rises sharply. The reason for this is an increase in the volume fraction of the β phase.
Ｃｒは、Ｎｂよりもβ相安定化能が高く、図３および図４に示す通り、Ｃｒ添加合金の方が低温度より多くのβ相が存在し焼結性が向上しやすい。そのため、図７ではＴｉ−４４Ａｌ−４ＣｒとＴｉ−４７Ａｌ−５Ｎｂとの間で、同じ相対密度を得るための温度に差がみられるが、β相が多くなることで焼結性が向上するという点では共通した効果が示されている。 Cr has a higher β-phase stabilizing ability than Nb, and as shown in FIGS. 3 and 4, the Cr-added alloy has more β phases than the low temperature, and the sinterability is likely to be improved. Therefore, in FIG. 7, there is a difference in temperature between Ti-44Al-4Cr and Ti-47Al-5Nb to obtain the same relative density, but it is said that the sinterability is improved by increasing the β phase. In terms of points, a common effect is shown.
（各相におけるＴｉおよびＡｌの拡散係数）
図８に、各相（α，γ，β）におけるＴｉ原子およびＡｌ原子の拡散係数を示す。同図において、縦軸が拡散係数（ｍ２／ｓ）、横軸（下）は温度の逆数（１／Ｔ）（１０−４Ｋ−１）、横軸（上）は温度（Ｋ）、▲（実線）がα相中でのＴｉ原子の拡散、△（破線）がα相中でのＡｌ原子の拡散、■（実線）がγ相中でのＴｉ原子の拡散、□（破線）がγ相中でのＡｌ原子の拡散、●（破線）がβ相中でのＴｉ原子の拡散、〇（実線）がβ相中でのＡｌ原子の拡散である。
(Diffusion coefficient of Ti and Al in each phase)
FIG. 8 shows the diffusion coefficients of Ti and Al atoms in each phase (α, γ, β). In the figure, the vertical axis is the diffusion coefficient (m 2 / s), the horizontal axis (bottom) is the inverse of the temperature (1 / T) (10 -4 K -1 ), and the horizontal axis (top) is the temperature (K). ▲ (solid line) is the diffusion of Ti atoms in the α phase, △ (broken line) is the diffusion of Al atoms in the α phase, ■ (solid line) is the diffusion of Ti atoms in the γ phase, and □ (broken line) is. The diffusion of Al atoms in the γ phase, ● (broken line) is the diffusion of Ti atoms in the β phase, and 〇 (solid line) is the diffusion of Al atoms in the β phase.
図８に示す通り、β相中のＴｉ原子およびＡｌ原子の拡散速度は、他の相（α，γ）よりも格段に速い。このことから、β相の体積率を高くして、焼結を行うことで、焼結現象が促進されることがわかる。拡散速度が速ければ、その分、焼結時間を短縮できる。拡散速度を速くすることで焼結密度を向上させられる。 As shown in FIG. 8, the diffusion rates of Ti and Al atoms in the β phase are much faster than those of the other phases (α, γ). From this, it can be seen that the sintering phenomenon is promoted by increasing the volume fraction of the β phase and performing sintering. The faster the diffusion rate, the shorter the sintering time. The sintering density can be improved by increasing the diffusion rate.
図８によれば、各相における拡散速度は、温度が低くなるとともに低下する。一方、拡散速度の速いβ相の体積率を高くできれば、焼結温度を下げた場合であっても十分量のＴｉ原子およびＡｌ原子が拡散され、促進された拡散により効率的に焼結が進行する。 According to FIG. 8, the diffusion rate in each phase decreases as the temperature decreases. On the other hand, if the volume fraction of the β phase, which has a high diffusion rate, can be increased, a sufficient amount of Ti atoms and Al atoms are diffused even when the sintering temperature is lowered, and the sintering proceeds efficiently due to the accelerated diffusion. do.
<付記>
以上説明した実施形態に記載のＴｉＡｌ基合金およびその製造方法は例えば以下のように把握される。
<Additional Notes>
The TiAl-based alloy described in the above-described embodiment and the method for producing the same are grasped as follows, for example.
本開示に係るＴｉＡｌ基合金の製造方法では、金属粉末射出成形法を用い、ＴｉＡｌ基合金の状態図からβ＋α／α変態温度（Ｔβ）を確認し、前記β＋α／α変態温度以上の温度で焼結する。 In the method for producing a TiAl-based alloy according to the present disclosure, a metal powder injection molding method is used, β + α / α transformation temperature (T β ) is confirmed from the state diagram of the TiAl-based alloy, and the temperature is equal to or higher than the β + α / α transformation temperature. Sinter.
β相存在温度域内では、温度が高くになるに従いβ相の体積率が大きくなる。高温域でのＴｉＡｌ基合金の構成相（α、γ、β）の中でも、β相は拡散係数が大きい。焼結は粒子内部の拡散、および粒界の拡散に依存する。拡散速度が速い方が焼結性は高くなる。すなわち、β相の体積率が高くなる温度域で焼結を実施することで、焼結現象が促進される。これにより、同じ相対密度の焼結体を得ようとした場合、焼結温度を下げる、または、焼結時間を短くすることが可能となる。 In the β-phase existing temperature range, the volume fraction of the β-phase increases as the temperature increases. Among the constituent phases (α, γ, β) of the TiAl-based alloy in the high temperature region, the β phase has a large diffusion coefficient. Sintering depends on the diffusion inside the particles and the diffusion of the grain boundaries. The faster the diffusion rate, the higher the sinterability. That is, the sintering phenomenon is promoted by performing sintering in a temperature range in which the volume fraction of the β phase is high. As a result, when trying to obtain a sintered body having the same relative density, it is possible to lower the sintering temperature or shorten the sintering time.
上記開示の一態様では、β安定化元素を添加することが望ましい。 In one aspect of the above disclosure, it is desirable to add a β-stabilizing element.
β安定化元素を添加すると、β相存在領域が低温側に拡大する。これによって、より低い温度でβの体積率を高くでき、焼結現象を促進させやすくなる。また、焼結温度を下げることで、融点との温度差を広げられるため、焼結時の変形を抑制できる。 When the β-stabilizing element is added, the β-phase presence region expands to the low temperature side. As a result, the volume fraction of β can be increased at a lower temperature, and the sintering phenomenon can be easily promoted. Further, by lowering the sintering temperature, the temperature difference from the melting point can be widened, so that deformation during sintering can be suppressed.
上記開示の一態様では、焼結性のみを考慮すればβ単相温度域内の温度で焼結することが望ましい。焼結合金の用途によって適正な組織を得るためには、（β＋α）２相領域内で焼結することもある。 In one aspect of the above disclosure, it is desirable to sinter at a temperature within the β single-phase temperature range in consideration of sinterability alone. In order to obtain an appropriate structure depending on the application of the sintered alloy, it may be sintered in the (β + α) two-phase region.
β単相温度域内では、拡散速度の速いβ相のみで構成されるため、β単相温度域内の温度で焼結することで、より焼結性を高めることが可能となる。相対密度９５％以上を容易に実現できる。 Since it is composed of only the β phase having a high diffusion rate in the β single phase temperature range, it is possible to further improve the sinterability by sintering at a temperature within the β single phase temperature range. A relative density of 95% or more can be easily realized.
上記開示の一態様では、前記焼結後、焼結温度よりも低く、かつ、前記β＋α／α変態温度以上のある温度で焼結体を所定時間保持してもよい。 In one aspect of the above disclosure, after the sintering, the sintered body may be held for a predetermined time at a temperature lower than the sintering temperature and higher than the β + α / α transformation temperature.
上記温度で焼結体を保持することで、Ｔｉ原子およびＡｌ原子の拡散を促進し、焼結性を高められる。 By holding the sintered body at the above temperature, the diffusion of Ti atoms and Al atoms can be promoted and the sinterability can be improved.
上記開示に係る製造方法で製造されたＴｉＡｌ基合金は、焼結密度の高い高品質な焼結体となる。 The TiAl-based alloy produced by the production method according to the above disclosure is a high-quality sintered body having a high sintering density.
Claims (5)
ＴｉＡｌ基合金の状態図からβ＋α／α変態温度を確認し、
前記β＋α／α変態温度以上のβ相存在温度域の温度で焼結するＴｉＡｌ基合金の製造方法。 A method for producing a TiAl-based alloy using a metal powder injection molding method.
Check the β + α / α transformation temperature from the phase diagram of the TiAl-based alloy.
A method for producing a TiAl-based alloy, which is sintered at a temperature in the β phase existence temperature range equal to or higher than the β + α / α transformation temperature.
A TiAl-based alloy produced by the method according to any one of claims 1 to 4.
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