钛合金(jin)激光(guang)送(song)丝(si)沉(chen)积增材制(zhi)造(zao)技术研(yan)究(jiu)进展

1、引言

将激(ji)光(guang)增(zeng)材制造技(ji)术(shu)用于(yu)钛(tai)合(he)金的(de)成形，能(neng)够(gou)降低(di)复杂结构(gou)钛合(he)金的加工成(cheng)本(ben)，具(ju)有(you)重(zhong)要(yao)的(de)工程价(jia)值(zhi)[1-3]，钛合金(jin)激光增(zeng)材制造(zao)也(ye)被(bei)业内(nei)认(ren)为(wei)是增材(cai)制造领域最具(ju)挑(tiao)战性的前沿发(fa)展方向之(zhi)一(yi)，并(bing)且(qie)存在(zai)不(bu)同(tong)方面(mian)的研究(jiu)热(re)点和难点[4-8]。钛(tai)合金激(ji)光(guang)增材(cai)制造(zao)可(ke)分为(wei)激光(guang)粉末选区成形(xing)和(he)激(ji)光(guang)同(tong)步(bu)材料送进成形(xing)两大(da)类(lei)，按(an)照(zhao)成(cheng)形机(ji)理(li)又(you)可细(xi)分(fen)为(wei)钛(tai)合(he)金(jin)选区(qu)激光(guang)熔化(hua)、钛合金(jin)激(ji)光(guang)送粉沉积和钛(tai)合金(jin)激光送(song)丝(si)沉积三(san)种(zhong)技术(shu)。基于合金(jin)粉末(mo)的前(qian)两(liang)种(zhong)增材(cai)制造(zao)技术(shu)成形(xing)精度高(gao)，适合加工(gong)形(xing)状复杂(za)的(de)小(xiao)型构(gou)件，但材料利(li)用率(lv)低(di)，而(er)且(qie)粉末对环(huan)境有一(yi)定(ding)污(wu)染(ran)，同时(shi)存(cun)在操(cao)作(zuo)环境要(yao)求(qiu)较高等诸多(duo)问题(ti)[9,10]。相较(jiao)而言(yan)，基(ji)于(yu)合(he)金丝(si)材(cai)的激光送丝沉积(ji)（Wire-feedingLaserMetalDeposition,WLMD）增材制(zhi)造(zao)技(ji)术的(de)材料(liao)利(li)用率很高(gao)且污(wu)染较少(shao)，更(geng)加经济实(shi)用，从(cong)而适(shi)合(he)大尺(chi)寸构(gou)件的(de)高(gao)效加工[11]。尤(you)其(qi)是对于(yu)未来(lai)争(zheng)相布局(ju)的太空(kong)金属增材(cai)制(zhi)造而言(yan)，激(ji)光送(song)丝设(she)备结构(gou)相对简(jian)单(dan)，丝(si)材(cai)更(geng)易(yi)存(cun)储运输(shu)，并且激(ji)光送丝(si)能够(gou)克服(fu)太(tai)空微(wei)重力环(huan)境的(de)影(ying)响[12,13]。因此，推(tui)动WLMD技术的(de)进一(yi)步发(fa)展具(ju)有重要(yao)应用价(jia)值和前瞻(zhan)意义。

选区(qu)激光熔化(hua)和(he)激(ji)光送粉沉(chen)积发展(zhan)较早(zao)，相(xiang)关(guan)研究报(bao)道较多，属于(yu)较(jiao)为(wei)成熟(shu)的钛(tai)合(he)金增材制(zhi)造(zao)技术[14,15]。激(ji)光(guang)送(song)丝(si)沉(chen)积则属于(yu)正在发(fa)展(zhan)的(de)增(zeng)材(cai)技术(shu)，其(qi)工程化应(ying)用还(hai)需(xu)工艺(yi)的(de)持续(xu)优化(hua)和完善(shan)，故具有较大(da)的研究空(kong)间(jian)。目前(qian)，钛(tai)合(he)金WLMD的研(yan)究主要(yao)集中在(zai)基础成(cheng)形(xing)工(gong)艺方面，其(qi)技(ji)术工艺(yi)还(hai)存在(zai)许(xu)多不(bu)足，缺少(shao)对(dui)于(yu)组织性能(neng)的(de)评价(jia)，并且(qie)缺(que)乏(fa)较(jiao)为(wei)系(xi)统(tong)的概(gai)括性(xing)进展(zhan)总(zong)结。因此，本文(wen)综述现阶(jie)段(duan)钛合(he)金WLMD技术的(de)基(ji)本(ben)原理(li)和工(gong)艺(yi)分类(lei)，讨论(lun)WLMD关(guan)键工艺(yi)参数、所成形(xing)钛(tai)合金的(de)组织(zhi)性能以(yi)及调控(kong)方(fang)法(fa)的(de)研究(jiu)进(jin)展，并展(zhan)望WLMD增材(cai)制造技(ji)术未(wei)来研究目标(biao)与发(fa)展趋(qu)势，以便为(wei)该技(ji)术(shu)后(hou)续(xu)研究(jiu)提供(gong)参考(kao)，促进(jin)其(qi)在(zai)更多(duo)领(ling)域的广泛应用(yong)。

2、激光送(song)丝(si)沉积(ji)技术成(cheng)形原(yuan)理(li)

WLMD以金(jin)属(shu)丝(si)材为原(yuan)材(cai)料，采用激(ji)光(guang)为热(re)源(yuan)熔(rong)化丝材并按规划路(lu)径进(jin)行生(sheng)产加(jia)工(gong)，耗时短(duan)且(qie)灵(ling)活性好。图1(a)是(shi)典(dian)型(xing)WLMD成形(xing)装(zhuang)置示(shi)意图，成(cheng)形装(zhuang)置(zhi)主要包(bao)括激(ji)光系(xi)统(tong)、控制(zhi)系(xi)统(tong)、沉(chen)积平(ping)台、保护气(qi)系统、送丝(si)机构(gou)以(yi)及机(ji)械(xie)臂(bi)几大(da)部分。开始打(da)印时，在(zai)控(kong)制系统(tong)命(ming)令下(xia)，保护气系统(tong)先(xian)行启动(dong)，为(wei)沉(chen)积(ji)过程提(ti)供(gong)真空(kong)气氛(fen)。在送(song)丝系统(tong)启(qi)动(dong)的(de)同时(shi)，激光(guang)系(xi)统(tong)发射激光(guang)将送(song)丝(si)嘴(zui)中(zhong)出来的(de)金(jin)属丝(si)熔(rong)化，金(jin)属(shu)丝材持(chi)续送(song)入(ru)熔池(chi)中(zhong)，实(shi)现(xian)熔化(hua)-凝(ning)固(gu)的(de)过程，同时(shi)机械臂(bi)按(an)照预先设定的路径移(yi)动(dong)，在金(jin)属基板上形成(cheng)沉积层(ceng)。如(ru)此(ci)不断(duan)循(xun)环(huan)，最(zui)终实现(xian)三(san)维立体(ti)零(ling)件的制(zhi)造[16-18]按(an)照(zhao)送丝方式的(de)不(bu)同，WLMD技(ji)术(shu)可以分(fen)为旁轴送(song)丝(si)和同轴(zhou)送丝(si)两(liang)种[19-21]。WLMD旁(pang)轴送丝，即金(jin)属(shu)丝(si)从(cong)激(ji)光束(shu)外(wai)通过送(song)丝机构(gou)输送(song)到(dao)激光束的焦(jiao)点上进(jin)行(xing)熔(rong)化，其平台搭建(jian)相对(dui)容(rong)易。然(ran)而(er)，由于(yu)熔(rong)覆过(guo)程(cheng)受到送丝方(fang)向(xiang)性(xing)的(de)限制，会(hui)影响(xiang)沉积(ji)过(guo)程中(zhong)沉(chen)积头(tou)的运(yun)动(dong)的(de)自由度，同(tong)时沉(chen)积(ji)过程(cheng)具(ju)有(you)明(ming)显的方(fang)向(xiang)性(xing)，所成(cheng)形(xing)的(de)沉(chen)积(ji)层尺(chi)寸(cun)和性(xing)能一致性较差，并且(qie)对(dui)光丝(si)的相对位(wei)置(zhi)的耦(ou)合性(xing)要(yao)求(qiu)较(jiao)高(gao)，如(ru)图(tu)1(b)所示[20]。WLMD同轴(zhou)送(song)丝(si)的(de)丝材由(you)激光(guang)中心送入(ru)，虽(sui)然(ran)可以有效避免(mian)送丝(si)方(fang)向性问(wen)题，但其(qi)重点主要(yao)在于激(ji)光(guang)焊枪的(de)设计和制造(zao)难(nan)度(du)大，这是因(yin)为(wei)焊枪(qiang)上集(ji)成(cheng)了(le)光路(lu)、气(qi)路、送(song)丝和(he)冷却等多(duo)种(zhong)功(gong)能(neng)，如图1(c)所(suo)示(shi)[21]，目前该技(ji)术正处(chu)于实(shi)验室到市(shi)场化的(de)拓展(zhan)阶(jie)段，因(yin)而属(shu)于较(jiao)新型(xing)的(de)增材(cai)制(zhi)造技(ji)术。

3、激光送(song)丝沉积技(ji)术及调(diao)控

3.1旁(pang)轴送(song)丝(si)技(ji)术

激光(guang)送丝增材(cai)制(zhi)造技术(shu)基(ji)于(yu)激光(guang)填(tian)丝(si)焊接技(ji)术(shu)发(fa)展(zhan)而来，因(yin)此(ci)，旁轴送丝(si)技术(shu)一直是(shi)WLMD领(ling)域(yu)的(de)主要研(yan)究(jiu)方向[22]。WLMD旁(pang)轴送丝工(gong)艺涉(she)及许多(duo)参数的变(bian)化(hua)，这些工(gong)艺参(can)数(shu)的改(gai)变(bian)会对沉积(ji)过程(cheng)有一定的(de)影响(xiang)。Mok等(deng)[23,24]较早(zao)采用(yong)半导体(ti)激光(guang)器送(song)丝(si)制备了TC4钛合(he)金，发(fa)现(xian)丝(si)材(cai)进(jin)入熔池的(de)方向(xiang)和角(jiao)度(du)等(deng)都(dou)会(hui)影(ying)响沉(chen)积(ji)层(ceng)的(de)表(biao)面光(guang)洁度(du)、沉积精(jing)度及(ji)显微(wei)组(zu)织(zhi)，沉(chen)积(ji)过(guo)程的扫描(miao)速(su)度、激(ji)光(guang)功率和(he)送丝速(su)度也会对沉(chen)积层组(zu)织(zhi)产生影响(xiang)，并(bing)导致成形(xing)件(jian)的力学(xue)性能(neng)发(fa)生(sheng)变化。

送丝(si)方(fang)向对WLMD旁(pang)轴送(song)丝成形效(xiao)果影(ying)响显著，相对(dui)于沉积(ji)方(fang)向会(hui)产生(sheng)前送(song)丝(si)、侧(ce)送丝(si)和(he)后送(song)丝三种方(fang)向，原理如(ru)图2(a)、(b)和(c)所示(shi)[25]。前(qian)送(song)丝方(fang)式(shi)是(shi)丝材从(cong)熔池(chi)前(qian)方(fang)送(song)入熔(rong)池(chi)进行(xing)熔(rong)化(hua)，熔(rong)化后的(de)金属(shu)液进入后(hou)方(fang)的熔池，后送(song)丝(si)方式(shi)与之(zhi)相反(fan)，侧送(song)丝方向(xiang)则(ze)介(jie)于前(qian)送丝(si)与后送(song)丝(si)之间。Kim等[26]认(ren)为(wei)前(qian)送(song)丝(si)方式(shi)下(xia)，即(ji)使(shi)送(song)丝(si)速度和位(wei)置公(gong)差很(hen)大(da)，丝(si)材也(ye)能(neng)完(wan)全熔化(hua)。同样地，Syed等(deng)[27]的(de)研究也表(biao)明前(qian)送(song)丝(si)比(bi)后(hou)送(song)丝(si)对(dui)送(song)丝速(su)度(du)和位(wei)置(zhi)具(ju)有更(geng)好的(de)适应性(xing)，在(zai)前(qian)送(song)丝时(shi)丝材被(bei)熔(rong)池(chi)散(san)发的(de)热(re)量(liang)熔(rong)化(hua)，对(dui)熔(rong)池(chi)的(de)扰(rao)动(dong)较(jiao)小并且丝(si)材(cai)反射(she)激光(guang)较少(shao)，因(yin)而(er)熔池(chi)表面光(guang)洁(jie)度较好(hao)，沉积(ji)层(ceng)内部(bu)致密(mi)且缺陷较少，而后(hou)送丝方式则带来(lai)较多的(de)缺陷。此外(wai)，Yang等(deng)[28]分析(xi)认(ren)为(wei)在(zai)前送丝时(shi)丝材(cai)不会阻(zu)挡(dang)激(ji)光作(zuo)用(yong)在基板上(shang)，基板(ban)可(ke)以(yi)获(huo)得(de)最大(da)的(de)热输(shu)入(ru)，并且(qie)熔滴在(zai)较(jiao)高温(wen)度基板(ban)上(shang)的(de)润湿(shi)度也(ye)能(neng)提(ti)高，从而(er)获得良(liang)好的表(biao)面(mian)质量(liang)。

Sun等(deng)[29]和(he)Shen等[30]的研(yan)究(jiu)也(ye)发现(xian)当(dang)送(song)丝位置在(zai)熔池(chi)的前方时成(cheng)形质(zhi)量较(jiao)高(gao)。与此(ci)同时(shi)，丝材对(dui)激(ji)光的(de)阻(zu)挡(dang)会使(shi)得熔池受(shou)热(re)不均(jun)匀(yun)，所(suo)以(yi)当丝(si)材(cai)接触(chu)点(dian)位(wei)于(yu)熔池前端(duan)时能(neng)够获得(de)较(jiao)好的(de)沉积效果，如(ru)图(tu)2(d)所示(shi)[28]。

不同的(de)送(song)丝(si)角度和位(wei)置也(ye)会(hui)产(chan)生(sheng)不同(tong)的(de)影响。Moures等(deng)[25]和(he)Mok等(deng)[24]研(yan)究结(jie)果(guo)表(biao)明，将(jiang)工(gong)艺定为前(qian)送(song)丝和(he)45°角度时，能(neng)够得(de)到最高(gao)的沉积速(su)率，并(bing)且试(shi)样表面(mian)光(guang)滑(hua)质(zhi)量较好(hao)。

Mortello等[31]发(fa)现(xian)，当丝(si)材高于(yu)熔池(chi)时(shi)，熔(rong)化的(de)金属(shu)液滴落(luo)入(ru)熔池时会使(shi)沉积(ji)层表(biao)面出(chu)现波纹(wen)，从(cong)而降低沉(chen)积(ji)层表(biao)面质量；但是(shi)当丝材(cai)与熔池相接触(chu)时，由于(yu)金属熔(rong)液传递模式(shi)由重(zhong)力驱动变为(wei)表(biao)面张力驱(qu)动，沉(chen)积(ji)工艺(yi)效(xiao)果也更加稳定(ding)。

尽管现(xian)在(zai)国(guo)内外(wai)的研(yan)究主要(yao)集(ji)中在旁轴送(song)丝(si)方(fang)案(an)上(shang)，但(dan)是仍然(ran)存在几(ji)点(dian)明显的(de)不足(zu)之(zhi)处，比(bi)如金属(shu)丝(si)材和激(ji)光(guang)束(shu)的位(wei)置(zhi)要(yao)求(qiu)高并(bing)且(qie)耦合性(xing)差，复(fu)杂零(ling)件(jian)成形(xing)时沉(chen)积头(tou)的自(zi)由度(du)会(hui)受(shou)到(dao)限制，以及会(hui)产生(sheng)送(song)丝方向性(xing)等问(wen)题(ti)。旁(pang)轴送(song)丝(si)方案(an)想要保(bao)持前(qian)送丝(si)沉积(ji)就(jiu)需(xu)要送丝喷嘴(zui)围(wei)绕熔(rong)覆(fu)头(tou)快速(su)旋转调整方(fang)向，或(huo)者(zhe)通过(guo)旋(xuan)转(zhuan)基体(ti)达(da)到保(bao)持前送丝(si)的(de)效(xiao)果。实际(ji)上，要解决(jue)旁轴送(song)丝方向问(wen)题，就(jiu)会增加(jia)机(ji)械(xie)设(she)计(ji)与控制(zhi)的(de)难(nan)度，而且(qie)调整方向需(xu)要更(geng)多(duo)的(de)时(shi)间(jian)，也(ye)会(hui)带(dai)来移(yi)动轨(gui)迹(ji)拐(guai)角处材料(liao)过渡堆积等(deng)问题(ti)[32]。

3.2同(tong)轴(zhou)送丝(si)技(ji)术

WLMD同(tong)轴送(song)丝(si)技术不存在(zai)送(song)丝(si)方(fang)向的问题，在拐(guai)角(jiao)等方向急(ji)剧(ju)变(bian)化(hua)的(de)特殊位(wei)置，仅(jin)需简(jian)单地(di)通过(guo)X和(he)Y轴的(de)加(jia)速(su)和(he)减速就(jiu)能(neng)实(shi)现(xian)过(guo)渡(du)，并且(qie)不(bu)会(hui)使(shi)得材(cai)料(liao)过渡(du)堆(dui)积，可以(yi)极(ji) 大(da)地(di)简(jian)化(hua)机(ji)械结构与电气控(kong)制(zhi)。目前(qian)主流(liu)的(de)激光同(tong)轴送(song)丝(si)技(ji)术(shu)可(ke)以根(gen)据(ju)分(fen)光(guang)的原理(li)分为三(san)种[33]，即分(fen)三(san)光束光(guang)内(nei)同轴技(ji)术、多(duo)光(guang)束集成光内(nei)同轴技(ji)术(shu)和(he)分环(huan)形光束(shu)光内(nei)同轴技术，其原(yuan)理和热源(yuan)分(fen)布(bu)如图3所示。德(de)国(guo)FraunhoferILT研究(jiu)所先(xian)后利用分三(san)光(guang)束(shu)和(he)分环(huan)形光(guang)束光(guang)内同轴技术(shu)制(zhi)造了(le)WLMD沉积设(she)备，并联合(he)Precitec公司推出了商用版分环形WLMD同轴送丝沉(chen)积设(she)备；而在国(guo)内，苏州大学利(li)用(yong)分三光(guang)束(shu)光(guang)内同(tong)轴(zhou)技(ji)术(shu)原理、重(zhong)庆绿(lv)色(se)智能技术研究所(suo)团队利用(yong)多光束(shu)集(ji)成(cheng)光(guang)内(nei)同(tong)轴(zhou)技术原理(li)分别(bie)研(yan)发了(le)用于(yu)实(shi)验室(shi)研(yan)究的(de)WLMD同轴送(song)丝(si)沉(chen)积设(she)备(bei)[16,34,35]。

由(you)于同(tong)轴(zhou)送(song)丝工(gong)艺(yi)的(de)特殊(shu)性(xing)，同轴送丝(si)技(ji)术(shu)的离(li)焦(jiao)量工艺(yi)窗口(kou)较窄(zhai)[36]。Ji等(deng)[37]发现(xian)当(dang)离焦量在-1.5~-2.5mm的范(fan)围(wei)内(nei)时(shi)才能形成(cheng)光(guang)滑(hua)连(lian)续的(de)熔(rong)道。当离焦(jiao)量过大(da)时，环形激光光(guang)斑孔径(jing)过大(da)，不(bu)足(zu)以充分(fen)熔化丝材，会(hui)形成(cheng)锯齿(chi)状熔道；而(er)当离(li)焦(jiao)量(liang)过小(xiao)时(shi)，环(huan)形激(ji)光光斑孔(kong)径过(guo)小(xiao)，激光(guang)能量(liang)集中(zhong)到丝材(cai)上(shang)，会(hui)使(shi)得(de)丝(si)材(cai)迅速(su)熔(rong)化成(cheng)熔(rong)滴并持续长(zhang)大(da)，最(zui)终形成不连续的滴(di)状(zhuang)熔(rong)道。为了(le)更(geng)好地分(fen)析(xi)熔(rong)道(dao)形状(zhuang)与(yu)送丝(si)工艺(yi)参数(shu)的关(guan)系(xi)，引入了(le)宽(kuan)高(gao)比(bi)和稀(xi)释率这两(liang)个关(guan)键(jian)指(zhi)标(biao)来(lai)评价(jia)熔(rong)道(dao)质量[38]。通(tong)常(chang)，扫描(miao)速(su)度(du)增(zeng)大，熔道的宽度(du)减(jian)小，而(er)熔道(dao)的高(gao)度(du)明(ming)显下降(jiang)，使(shi)得(de)宽高(gao)比(bi)增大(da)；激(ji)光(guang)功(gong)率(lv)增(zeng)大(da)，激(ji)光(guang)光(guang)斑的(de)能(neng)量密度(du)也(ye)增(zeng)大，熔(rong)道的(de)宽度(du)和(he)深(shen)度也随(sui)之(zhi)增大(da)，使(shi)得熔(rong)道(dao)的(de)稀(xi)释率增(zeng)大[34]。相对(dui)来(lai)说，送丝速(su)度对熔(rong)道的(de)高(gao)度影响(xiang)更(geng)显(xian)著(zhu)，送丝(si)速度(du)的增(zeng)加能够提(ti)高金属(shu)丝材的(de)供给量，使得熔(rong)高(gao)显(xian)著增(zeng)加(jia)[16]。为了更(geng)好地理解(jie)激(ji)光功率的(de)影(ying)响(xiang)，图(tu)4提(ti)出(chu)了(le)一种预测(ce)同(tong)轴(zhou)送丝(si)工艺(yi)激(ji)光功(gong)率(lv)密度的(de)模型[39]，可(ke)模(mo)拟(ni)打印(yin)过程中(zhong)任(ren)何表面(mian)上任意(yi)数量的(de)光束和功率密(mi)度，并(bing)且能预测(ce)各种工(gong)艺(yi)参数(shu)下(xia)激(ji)光光斑(ban)的(de)形状(zhuang)和(he)大小，从(cong)而(er)有(you)助于(yu)优化(hua)打印轨迹和制造(zao)策(ce)略(lve)。

针(zhen)对钛(tai)合(he)金(jin)的WLMD同(tong)轴送(song)丝打(da)印(yin)，德(de)国(guo)的(de)FraunhoferILT研究(jiu)所、勃兰登(deng)堡工(gong)业大(da)学(xue)和(he)西班牙(ya)工(gong)业研究中(zhong)心(xin)等先(xian)后(hou)对TC4合(he)金进(jin)行(xing)了(le)探索(suo)[40-42]，成功(gong)实(shi)现了钛(tai)合金(jin)典型(xing)结构(gou)的(de)增材(cai)制造(zao)。Kelbassa等(deng)[40]利(li)用连续环(huan)形(xing)激光束(shu)开(kai)展(zhan)同(tong)轴送(song)丝WLMD试(shi)验，将(jiang)惰(duo)性气体通(tong)过(guo)同轴(zhou)方式输送，避免熔(rong)池暴(bao)露在空气(qi)中发生氧化(hua)，如(ru)图5所(suo)示(shi)。这种设计同(tong)时能(neng)够减少沉积头(tou)的集(ji)成质(zhi)量(liang)，使得(de)沉积(ji)头具(ju)有(you)高(gao)动(dong)态的(de)特(te)征，加(jia)上纤细(xi)的Ti-6Al-4V丝材(cai)原(yuan)料，可(ke)以(yi)近(jin)净成(cheng)形(xing)复杂(za)的几何形状(zhuang)。中国(guo)船(chuan)舶七二(er)五(wu)所和上(shang)海(hai)产业(ye)技术(shu)研(yan)究院分(fen)别(bie)利(li)用(yong)Precitec分环形激(ji)光同(tong)轴送丝(si)沉(chen)积设(she)备对(dui)钛(tai)合金(jin)零部(bu)件增材制造(zao)工艺进行(xing)探索(suo)[43]，其(qi)中对直径1.0~1.6mm钛合(he)金丝(si)材研(yan)究表(biao)明，当激(ji)光器功率为(wei)3000W，熔(rong)敷效率(lv)可达5~30g/min。而Du等[44]研(yan)究了(le)真(zhen)空(kong)条(tiao)件(jian)对WLMD同轴送(song)丝制(zhi)造Ti-6Al-4V薄壁(bi)件(jian)的作用(yong)，发(fa)现(xian)沉积(ji)过程(cheng)中(zhong)的高度(du)增量(liang)应(ying)在适当范围内(nei)，并与(yu)层高相(xiang)匹配(pei)；当层(ceng)间冷(leng)却(que)时(shi)间(jian)为(wei)1s时，热(re)积(ji)累量较大(da)，在(zai)高激光功率(lv)、层间(jian)冷(leng)却(que)时间(jian)大于(yu)5s的(de)条件下(xia)，薄壁件(jian)层(ceng)宽更容易保(bao)持(chi)一(yi)致性(xing)。

尽(jin)管(guan)同(tong)轴(zhou)送(song)丝(si)方(fang)案(an)具有(you)诸(zhu)多优(you)点，但是当前对(dui)于WLMD同(tong)轴(zhou)送(song)丝(si)技术(shu)的研究总体仍(reng)然(ran)较少，其难点(dian)主(zhu)要(yao)在于光(guang)路(lu)的转换难度(du)较(jiao)高，比如(ru)，将(jiang)实(shi)心光束(shu)转(zhuan)换(huan)为(wei)分(fen)环(huan)形光(guang)束，同时金属(shu)丝(si)要避(bi)开(kai)环(huan)形光束并从(cong)中(zhong)心送(song)进，完(wan)成这一过(guo)程需要(yao)考(kao)虑(lv)不同光路、汇聚(ju)角(jiao)度(du)、光(guang)斑内外(wai)径等(deng)对(dui)丝(si)材的影(ying)响。此外(wai)，采用该方(fang)案时(shi)激(ji)光(guang)功(gong)率与(yu)送(song)丝速(su)度(du)的匹配(pei)要(yao)求(qiu)会(hui)更(geng)高，否则(ze)容(rong)易(yi)出(chu)现丝材与熔池底(di)部(bu)相撞使得(de)丝材弯曲，使(shi)熔(rong)池不稳(wen)定(ding)，从(cong)而(er)影响成形质(zhi)量(liang)。

4、激(ji)光(guang)送(song)丝沉(chen)积钛合(he)金(jin)组(zu)织、性(xing)能(neng)及(ji)调(diao)控

4.1激(ji)光送(song)丝(si)沉(chen)积(ji)钛(tai)合(he)金的组(zu)织(zhi)特(te)征

尽(jin)管(guan)WLMD在(zai)成形(xing)工(gong)艺(yi)方(fang)面(mian)具(ju)有(you)特殊优势(shi)，但沉(chen)积的(de)试样(yang)普遍存(cun)在(zai)气孔(kong)、未熔(rong)合、应(ying)力(li)和(he)组(zu)织性能(neng)不均(jun)匀等问题[45]。因(yin)此(ci)，成形样品(pin)的组(zu)织(zhi)演(yan)变(bian)机(ji)理和性能(neng)调控方法(fa)仍(reng)然(ran)是WLMD技(ji)术(shu)近(jin)年(nian)来(lai)的研究重(zhong)点(dian)。由(you)于(yu)激光熔(rong)化(hua)沉积时(shi)熔池(chi)内部(bu)热质传(chuan)输过程(cheng)较为复杂，因(yin)此对(dui)沉积(ji)过程(cheng)中(zhong)钛(tai)合(he)金显(xian)微(wei)组织(zhi)的(de)演(yan)变行(xing)为(wei)开展研究(jiu)，将(jiang)有利(li)于建立(li)WLMD钛合(he)金(jin)的组织(zhi)和(he)性(xing)能(neng)映(ying)射(she)关系。

研究者们[46-48]发现WLMD成形样品(pin)的(de)组(zu)织形(xing)貌(mao)具有(you)很(hen)大(da)的(de)相似性，其沉积(ji)层(ceng)通常(chang)为(wei)柱状(zhuang)晶(jing)，顶部为等轴(zhou)晶(jing)。沉(chen)积过程(cheng)类(lei)似于(yu)铸造(zao)当中(zhong)的(de)定(ding)向(xiang)凝(ning)固(gu)，熔(rong)池(chi)底(di)部由于较(jiao)大(da)的温(wen)度(du)梯(ti)度(du)的(de)作用(yong)，会在(zai)前(qian)一(yi)层的基(ji)础(chu)上发生(sheng)外延生长，从(cong)而(er)形成穿(chuan)过两(liang)个或者多个沉积层(ceng)的柱状(zhuang)晶(jing)，而(er)在熔(rong)池(chi)顶(ding)部会(hui)形(xing)成(cheng)等轴晶(jing)，这是(shi)由于顶部与空气接触从而(er)能较快冷却(que)。相(xiang)似地(di)，钛合金的(de)增材制(zhi)造(zao)组织(zhi)中(zhong)常见问题是，沿(yan)着试样(yang)沉(chen)积(ji)的(de)方向(xiang)，会(hui)生成(cheng)粗(cu)大(da)的(de)初生β柱状晶(jing)粒(li)，对(dui)于(yu)WLMD钛(tai)合金(jin)而(er)言(yan)，β柱(zhu)状晶(jing)粒(li)长(zhang)度(du)能(neng)达到几百微米(mi)或几(ji)个(ge)毫米[49]。此(ci)外(wai)，晶界的(de)两(liang)侧存在密集排列(lie)的(de)针片状α相(xiang)，一(yi)般(ban)是(shi)由晶(jing)界(jie)处(chu)形(xing)核(he)并向晶(jing)内生长(zhang)而成(cheng)，由于(yu)晶界α相(xiang)在横向(xiang)载(zai)荷(he)作用(yong)下(xia)会(hui)使(shi)得材料过早断(duan)裂(lie)，从而(er)显(xian)著地(di)影(ying)响成形件(jian)的塑(su)性(xing)变(bian)形(xing)行为(wei)[50]。也(ye)就是(shi)说，钛合金(jin)熔(rong)池内(nei)部(bu)存(cun)在的(de)明显(xian)温度(du)梯(ti)度(du)，使得(de)初(chu)生(sheng)β柱(zhu)状晶(jing)粒(li)沿(yan)温(wen)度梯度(du)方向(xiang)的(de)定向(xiang)生(sheng)长通(tong)常(chang)会(hui)形成较(jiao)强(qiang)的(de)<001>织(zhi)构(gou)，并(bing)产生(sheng)α转变织构(gou)，从(cong)而对疲劳(lao)性(xing)能(neng)产(chan)生不(bu)利(li)影响(xiang)，同时(shi)使得力(li)学(xue)性能出(chu)现(xian)各向异性(xing)[51]。

对于(yu)工业(ye)上应用最(zui)多的(α+β)型(xing)钛合金，其组(zu)织演变过程(cheng)一般(ban)如下(xia)[52]：沉积(ji)层凝(ning)固时，内部首先(xian)发(fa)生(sheng)液(ye)相(xiang)→β相(xiang)的相变。随(sui)着温度持续降(jiang)低，β相稳定元(yuan)素(su)扩散系(xi)数(shu)较大而使得(de)原(yuan)始(shi)β晶(jing)粒(li)不(bu)断(duan)长(zhang)大，并(bing)将晶内的(de)α相(xiang)稳定元(yuan)素持续(xu)排到晶(jing)界(jie)处(chu)。一旦(dan)温度降(jiang)低至(zhi)α+β两(liang)相(xiang)区时，将(jiang)发生(sheng)β→α转(zhuan)变(bian)。由(you)于β晶(jing)界(jie)处富集(ji)了α相稳定元(yuan)素(su)，导(dao)致(zhi)α相(xiang)在(zai)β相(xiang)晶界上(shang)形(xing)核(he)，并沿(yan)晶(jing)界形(xing)成(cheng)连(lian)续的(de)α相层(ceng)，即晶界(jie)α相(xiang)。当冷(leng)却(que)速率(lv)较(jiao)慢(man)时，晶(jing)界(jie)α相(xiang)会逐(zhu)渐(jian)在(zai)β晶(jing)粒(li)内部形成(cheng)平(ping)行的片(pian)状(zhuang)α相(xiang)，并与其它(ta)的片(pian)状(zhuang)α相交(jiao)织(zhi)从而停止(zhi)进(jin)一步生(sheng)长。如(ru)图6所(suo)示为(α+β)钛合(he)金(jin)冷(leng)却时(shi)的(de)相(xiang)变(bian)化(hua)曲线以(yi)及(ji)WLMD钛(tai)合金典型组织(zhi)形貌，合(he)金(jin)在冷却(que)速(su)度较高时(shi)内部基(ji)本(ben)为马(ma)氏(shi)体结构(gou)，但(dan)随着(zhe)冷(leng)却(que)速(su)度降低(di)到410℃/s以下时(shi)，魏(wei)氏体会逐渐(jian)代(dai)替(ti)马氏(shi)体(ti)结(jie)构[46,53,54]。

简(jian)言之，WLMD试样(yang)内部(bu)通(tong)常(chang)由(you)粗(cu)大的β柱(zhu)状晶(jing)、晶(jing)界(jie)α相(xiang)、晶内片层(ceng)状(zhuang)α集束(shu)以(yi)及少(shao)量(liang)马氏(shi)体(ti)相组(zu)成。考(kao)虑到(dao)魏氏组织(zhi)和(he)马(ma)氏体(ti)力(li)学性(xing)能较差(cha)，WLMD钛合金理(li)想的(de)组织(zhi)为较(jiao)小(xiao)尺(chi)寸的(de)初生β晶(jing)粒(li)，以(yi)及(ji)尽(jin)可能多(duo)的(de)α集(ji)束和网篮(lan)组(zu)织[55]。然而(er)，不(bu)同的(de)复(fu)合工艺(yi)和环(huan)境会对WLMD组(zu)织产(chan)生(sheng)影(ying)响(xiang)。Guo等(deng)[56]将(jiang)电(dian)弧和(he)激(ji)光增(zeng)材制(zhi)造进(jin)行复合时，所(suo)成形的TC11钛(tai)合(he)金(jin)在(zai)沉积(ji)状态(tai)下(xia)微观组(zu)织(zhi)主要是由层(ceng)状α团(tuan)簇(cu)组(zu)成的魏(wei)氏(shi)组(zu)织(zhi)。固溶时效处(chu)理(li)后(hou)，组(zu)织转(zhuan)变为条形(xing)α、β相(xiang)和(he)细针状(zhuang)马氏(shi)体相组(zu)成(cheng)的网(wang)篮(lan)形(xing)态，水(shui)淬后形(xing)成(cheng)大(da)量的(de)αs次生(sheng)相和α′马(ma)氏(shi)体相(xiang)，与(yu)此(ci)同(tong)时，α相(xiang)和β相(xiang)的尺(chi)寸(cun)会(hui)由(you)于(yu)空冷而变(bian)粗大。而Guo等(deng)[57]采用(yong)如(ru)图7所示(shi)的(de)水(shui)下(xia)WLMD技(ji)术，通过(guo)增加(jia)保护(hu)气体流(liu)量到80L/min，同(tong)时(shi)热(re)输入从(cong)1.75kJ/cm提高(gao)到2.5kJ/cm，获得了(le)均匀无氧(yang)化的(de)水(shui)下(xia)熔(rong)覆(fu)层；随着热输(shu)入(ru)量的增(zeng)加，α板条的晶粒尺寸和(he)厚度(du)增(zeng)加(jia)，α′的(de)含(han)量减少，氧化现(xian)象(xiang)也有(you)所(suo)改(gai)善，但柱状β晶粒(li)和(he)球形β晶粒(li)尺(chi)寸(cun)均增大。不同(tong)热输入(ru)层(ceng)的(de)显微组织(zhi)由(you)不同尺寸的(de)片层α相和针状α′相组成(cheng)。此(ci)外，冷却(que)速率(lv)的降(jiang)低抑制了(le)针状(zhuang)马(ma)氏(shi)体(ti)的(de)单向生(sheng)长，使马(ma)氏(shi)体(ti)的排(pai)列(lie)接近(jin)无(wu)序(xu)状态，熔(rong)覆层的(de)变(bian)形更(geng)加(jia)均(jun)匀，有效(xiao)地防(fang)止了裂(lie)纹的扩(kuo)展。

4.2激光送丝(si)沉(chen)积(ji)钛合金(jin)的性能(neng)及调(diao)控

由(you)于WLMD钛(tai)合(he)金(jin)内部组织分(fen)布不(bu)均而(er)使各个(ge)位(wei)置力学性能出(chu)现(xian)差异。通常试(shi)样硬度受沉积工艺(yi)参数的影响(xiang)较(jiao)小，而(er)拉(la)伸性(xing)能(neng)则(ze)在垂直(zhi)和平(ping)行(xing)基(ji)板(ban)的方(fang)向上(shang)表现(xian)出(chu)较(jiao)大差别，主要(yao)在(zai)于(yu)垂(chui)直方(fang)向的延(yan)伸(shen)率优于平行方向。这(zhe)是因(yin)为平(ping)行(xing)方向(xiang)有着更(geng)多(duo)的(de)β柱状(zhuang)晶(jing)界，晶界处的(de)α相(xiang)在载(zai)荷作(zuo)用下会提前(qian)失(shi)效(xiao)。沉积工艺(yi)参数(shu)会对(dui)熔(rong)池(chi)热输入(ru)产生重(zhong)要影响，进(jin)而形(xing)成(cheng)不同(tong)的(de)组织形貌(mao)，并对沉积试(shi)样的(de)性能(neng)产(chan)生(sheng)关键(jian)作用。因(yin)此，利(li)用沉(chen)积过(guo)程(cheng)中以及(ji)沉积(ji)完成后(hou)的各种工(gong)艺(yi)手段(duan)对(dui)组织(zhi)进(jin)行(xing)优化，有(you)助于(yu)获(huo)得(de)较好性能(neng)的合金(jin)，对此(ci)已(yi)有(you)大量组织性(xing)能(neng)调控相(xiang)关(guan)的(de)研(yan)究[58]。表(biao)1为(wei)不(bu)同成形技术所(suo)制(zhi)备钛合(he)金力学性能(neng)的(de)对(dui)比(bi)，可见(jian)，送(song)丝增材制(zhi)造钛(tai)合(he)金(jin)构件的力学(xue)性(xing)能(neng)受(shou)控于工艺，因(yin)而(er)高性(xing)能(neng)构件(jian)的增(zeng)材(cai)制造需要(yao)建立(li)材(cai)料-工(gong)艺(yi)-组(zu)织-性能的(de)一体化(hua)设计(ji)、制(zhi)造与(yu)调控理论(lun)及(ji)方法。

激(ji)光(guang)增(zeng)材制造成形过(guo)程(cheng)中繁(fan)杂的热(re)循(xun)环以(yi)及(ji)残(can)余应(ying)力分布，会(hui)在(zai)沉积层中产生较为(wei)严(yan)重的(de)变(bian)形甚(shen)至开(kai)裂(lie)，从而(er)对性(xing)能(neng)产生关键的(de)影响，而(er)数值(zhi)模拟是解决(jue)该(gai)类(lei)问题的有力(li)工(gong)具。任(ren)朝晖(hui)等[63]对钛(tai)合金WLMD过(guo)程(cheng)中(zhong)的温度(du)场和(he)应力(li)场开展了模(mo)拟(ni)研究，采用(yong)ABAQUS软件建立(li)完全(quan)热力(li)耦合的(de)有(you)限(xian)元(yuan)模型(xing)，研(yan)究了(le)Ti-6Al-4V单道(dao)多层沉积(ji)件(jian)的(de)热(re)循环(huan)特(te)性和(he)应力分(fen)布(bu)，如图(tu)8所示，发(fa)现随(sui)着沉积(ji)层(ceng)数的(de)增(zeng)加，热累积效(xiao)应(ying)逐渐变(bian)强(qiang)，且(qie)冷(leng)却速率下(xia)降；薄(bao)壁(bi)沉(chen)积件(jian)整体的残余(yu)应(ying)力(li)为拉应(ying)力(li)状态，x方向(xiang)明显大于(yu)另(ling)外两(liang)个方(fang)向(xiang)，然而垂直(zhi)于扫(sao)描方(fang)向(xiang)较(jiao)易产(chan)生裂(lie)纹(wen)等缺陷(xian)；同时(shi)，中(zhong)部(bu)残(can)余应力相对稳定，最大残余(yu)应力(li)集(ji)中在(zai)沉(chen)积层(ceng)两(liang)端与(yu)基板交(jiao)界(jie)处。

为了进(jin)一步(bu)调(diao)控组(zu)织(zhi)性能(neng)，Ye等(deng)[64]利(li)用(yong)超声(sheng)微(wei)锻造(zao)对(dui)WLMD钛(tai)合(he)金(jin)进行研(yan)究(jiu)，结(jie)果(guo)表(biao)明(ming)，振幅和锻造力会使(shi)得(de)Ti-6Al-4V试(shi)样中(zhong)出(chu)现大量(liang)等轴(zhou)β晶(jing)粒(li)，其形(xing)态也可以通过(guo)工(gong)艺参(can)数进(jin)行控(kong)制，如(ru)图(tu)9所示，随(sui)着振(zhen)幅的(de)增(zeng)大(da)，等(deng)轴β晶粒平均(jun)尺寸减(jian)小(xiao)；随(sui)着锻造力(li)的(de)增加，沉积层(ceng)与(yu)基(ji)板界(jie)面处(chu)的(de)缺陷(xian)数(shu)量增加(jia)，但显(xian)微(wei)硬(ying)度也随之增大(da)。Yang等[65]研究(jiu)了(le)超(chao)声(sheng)冲(chong)击(ji)前(qian)后成形样品的变化(hua)，发(fa)现超(chao)声(sheng)冲击(ji)后(hou)的样(yang)品残余(yu)应力远低于(yu)沉积态样品，同时(shi)提高了拉伸强(qiang)度(du)，但(dan)伸长率(lv)有所(suo)降(jiang)低(di)。Donoghue等(deng)[66]将(jiang)轧(ya)制与沉积(ji)进行工(gong)艺复(fu)合(he)，发现(xian)每一(yi)层(ceng)沉积(ji)后只(zhi)需(xu)较(jiao)低(di)的变形量(liang)就能(neng)显(xian)著地减小晶(jing)粒尺(chi)寸(cun)，并(bing)且(qie)β和(he)α相织(zhi)构(gou)也(ye)大幅(fu)降低到(dao)接近随(sui)机分布，同时(shi)这些破(po)碎(sui)晶粒可以在后一(yi)层(ceng)沉积(ji)过程(cheng)中再(zai)次(ci)加热(re)时作为再结晶晶(jing)核。Sabban等[67]通过在(zai)接(jie)近(jin)但(dan)低于β转变温度的条(tiao)件(jian)下循(xun)环(huan)热(re)处理(li)TC4钛(tai)合(he)金(jin)，使(shi)得针(zhen)片(pian)状α相逐渐(jian)转(zhuan)变(bian)为球状(zhuang)，球形(xing)化双(shuang)相(xiang)组织将沉积试样(yang)的(de)延展性(xing)提高(gao)了(le)80%，韧性提(ti)高(gao)了(le)66%。除(chu)此(ci)之外，还(hai)有(you)固(gu)溶时(shi)效(xiao)热处理[68,69]、电(dian)脉(mai)冲热(re)处理[70]和(he)等(deng)通(tong)道角(jiao)挤压[71]等(deng)方式(shi)来(lai)改(gai)善(shan)合金(jin)组(zu)织(zhi)，从(cong)而(er)对(dui)力学性(xing)能进(jin)行调(diao)控。

越(yue)来越(yue)多(duo)致(zhi)力于钛合金WLMD增材(cai)制(zhi)造(zao)技术(shu)工(gong)程化应(ying)用(yong)的基础(chu)研(yan)究正在(zai)持续开展。笔者(zhe)研(yan)究(jiu)团队同样(yang)注重发展(zhan)WLMD基础(chu)工艺(yi)和成(cheng)形钛(tai)合金(jin)组(zu)织(zhi)性(xing)能优化(hua)方法，并且基(ji)于新(xin)一(yi)代(dai)航空(kong)航(hang)天(tian)大(da)型关(guan)键承(cheng)力(li)构(gou)件(jian)的一体化、轻(qing)量(liang)化和高可靠(kao)等(deng)设计(ji)使用要求(qiu)，正在进行(xing)高(gao)效高(gao)精(jing)度(du)激光增材(cai)制(zhi)造技(ji)术的(de)创(chuang)新开(kai)发(fa)，其(qi)中的关(guan)键科学问题(ti)和技术问(wen)题(ti)均涉(she)及(ji)结构、材(cai)料、工艺、装(zhuang)备(bei)等多(duo)因素的耦合(he)、匹(pi)配及调控。

5、结论

相(xiang)较(jiao)于传统钛合(he)金(jin)加工工(gong)艺(yi)，钛(tai)合金(jin)WLMD具有(you)节约(yue)原(yuan)材料、降低生(sheng)产成(cheng)本(ben)、提高生(sheng)产(chan)效率(lv)以(yi)及(ji)实(shi)现(xian)复(fu)杂(za)结(jie)构(gou)成形等(deng)优势，是钛(tai)合(he)金(jin)现代制造(zao)技术的一个(ge)重(zhong)要发展(zhan)方向(xiang)，并具(ju)有广(guang)阔(kuo)的研究(jiu)价值(zhi)和应(ying)用(yong)前景(jing)。但(dan)是(shi)，在(zai)沉(chen)积(ji)过程(cheng)中还(hai)有复(fu)合(he)成(cheng)形(xing)工艺、成形(xing)件(jian)精(jing)度、表面(mian)质量(liang)、组织控制、应(ying)力控制(zhi)和复杂路(lu)径规(gui)划等许(xu)多(duo)问(wen)题亟待(dai)解决(jue)，而(er)正是(shi)这些因(yin)素(su)的(de)协同(tong)优(you)化(hua)决定了WLMD钛(tai)合金成(cheng)形(xing)件(jian)是(shi)否满足工程(cheng)应用(yong)的(de)需(xu)求(qiu)。WLMD技术(shu)未(wei)来应当(dang)着(zhe)重面(mian)向(xiang)航空(kong)航(hang)天大(da)型(xing)复杂(za)构(gou)件制(zhi)造(zao)、太(tai)空(kong)金属(shu)增材(cai)制(zhi)造、舰载(zai)增材制(zhi)造(zao)、水(shui)下激(ji)光修复等领(ling)域发(fa)挥(hui)其独(du)特(te)优势(shi)。钛(tai)合(he)金WLMD具有(you)丰(feng)富(fu)的(de)科学内(nei)涵，总结发(fa)展现状(zhuang)并(bing)思(si)考(kao)其(qi)未来研究(jiu)趋势，主(zhu)要结论和(he)需(xu)进一步(bu)关注的(de)方(fang)向(xiang)如(ru)下(xia)：

（1）WLMD高(gao)效率(lv)和高(gao)精(jing)度(du)复合增(zeng)材制(zhi)造(zao)。旁(pang)轴送(song)丝WLMD受(shou)限(xian)于方向耦(ou)合问(wen)题，而发展同(tong)轴(zhou)送丝(si)WLMD工艺需(xu)要(yao)重(zhong)点克(ke)服加(jia)工(gong)装(zhuang)备集(ji)成(cheng)设(she)计(ji)的(de)难题。此外，当(dang)前仍以单(dan)一激光成形钛合金为(wei)主(zhu)，但是(shi)受(shou)限于激(ji)光功(gong)率和(he)成形质量的匹(pi)配(pei)性问题，WLMD成形(xing)效率(lv)仍有较(jiao)大提(ti)升空间(jian)。为此(ci)，需研究(jiu)增材制(zhi)造(zao)过(guo)程(cheng)中(zhong)多波长(zhang)激光集成、丝材(cai)-粉(fen)末多(duo)材料(liao)复合(he)、多(duo)能场(chang)-多工(gong)艺的(de)匹(pi)配协调(diao)机制，建(jian)立(li)构件(jian)成形质(zhi)量主(zhu)动控制(zhi)数(shu)学(xue)模型及控制(zhi)策(ce)略(lve)，实现(xian)高(gao)功(gong)率激光(guang)送(song)丝(si)沉(chen)积、激光熔池(chi)动(dong)态整形以及激光送粉熔覆(fu)多工(gong)艺(yi)协同(tong)高效高精度(du)分区制造(zao)。其(qi)中(zhong)，为消(xiao)除送(song)丝(si)方向(xiang)性问(wen)题，可(ke)进(jin)一(yi)步开展(zhan)新型同轴送(song)丝技(ji)术(shu)的(de)开(kai)发(fa)，提(ti)高(gao)装(zhuang)备(bei)和(he)工艺(yi)稳(wen)定(ding)性。

（2）WLMD过(guo)程(cheng)组(zu)织(zhi)缺陷(xian)识(shi)别、反(fan)馈与(yu)自调节。成(cheng)形(xing)工(gong)艺对(dui)组织宏(hong)微(wei)观(guan)形貌和应力(li)分布(bu)影响显著(zhu)，为(wei)满(man)足(zu)工(gong)艺(yi)不断(duan)优化(hua)发(fa)展的需(xu)求，有(you)必(bi)要对成(cheng)形(xing)过程中的未熔(rong)合(he)、裂(lie)纹和气孔(kong)等缺(que)陷(xian)进行(xing)监(jian)测。为(wei)此(ci)，需构建(jian)一(yi)种高精度在线(xian)实(shi)时监(jian)测与(yu)反(fan)馈优(you)化(hua)智能感(gan)知系统，通过在(zai)线精(jing)准监测(ce)装(zhuang)置(zhi)对多束(shu)高(gao)功率(lv)激光(guang)增(zeng)材(cai)制造(zao)凝固成型的沉积(ji)层(ceng)质(zhi)量进行(xing)实(shi)时监(jian)测，并结(jie)合(he)高(gao)准确(que)度(du)离线检测技(ji)术(shu)对比(bi)纠正，通(tong)过(guo)工(gong)艺(yi)调(diao)整(zheng)、熔池(chi)整(zheng)形(xing)、轨(gui)迹优化(hua)及局(ju)部(bu)重(zhong)熔等(deng)方法(fa)在(zai)线完成缺(que)陷的(de)主动(dong)控(kong)制，实(shi)现(xian)缺(que)陷在线精准(zhun)识别(bie)-实(shi)时(shi)诊断(duan)与(yu)反(fan)馈(kui)-缺(que)陷主动(dong)抑(yi)制(zhi)的(de)闭(bi)环(huan)自调节(jie)。

（3）WLMD晶粒细化技术(shu)与(yu)相结(jie)构调控(kong)。WLMD沉积(ji)组(zu)织往(wang)往由(you)粗大(da)的(de)β柱(zhu)状(zhuang)晶、晶界(jie)α相(xiang)、晶(jing)内(nei)片(pian)层(ceng)状α集(ji)束(shu)以及(ji)少(shao)量(liang)马氏体(ti)相组(zu)成(cheng)，为(wei)了(le)获(huo)得较(jiao)佳(jia)的(de)性能参数，需(xu)要建并完善(shan)材(cai)料-工艺(yi)-组织(zhi)-性能的(de)一(yi)体(ti)化设(she)计(ji)、制(zhi)造(zao)与调控(kong)理(li)论及方(fang)法(fa)。为(wei)解决WLMD钛(tai)合金(jin)组织(zhi)的(de)不(bu)均匀(yun)性(xing)，提(ti)高成形件(jian)综合(he)力(li)学性(xing)能(neng)，可以(yi)从(cong)材料(liao)成(cheng)分(fen)元(yuan)素设(she)计与(yu)控(kong)制(zhi)，以及沉(chen)积(ji)工艺(yi)参(can)数(shu)优(you)化与(yu)调控(kong)等方(fang)面入手(shou)；为解(jie)决(jue)(α+β)型(xing)钛合(he)金内(nei)部(bu)由(you)于增材制(zhi)造快速(su)冷(leng)却(que)导(dao)致的(de)亚稳(wen)态(tai)马氏体(ti)含量过多，可采(cai)用合适的(de)后处(chu)理方式(shi)，包括引(yin)入(ru)颗粒、超声(sheng)冲击和(he)多(duo)重(zhong)热(re)处理等方法，使马(ma)氏体转(zhuan)化为稳(wen)定(ding)的α相，获得(de)更(geng)多网篮组织(zhi)，提高合(he)金(jin)的(de)力学(xue)性能并(bing)改善(shan)各向异(yi)性。

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